{"loaderData":{"root":{"topics":[{"slug":"accessibility","title":"Accessibility","track":"Frontend","covers":null,"summaryHtml":"Building interfaces everyone can use: semantics, the accessibility tree, ARIA, keyboard and focus, and WCAG. Senior frontend interviews expect it, and it's the area where \"it works for me\" answers fail most visibly.","summaryText":"Building interfaces everyone can use: semantics, the accessibility tree, ARIA, keyboard and focus, and WCAG. Senior frontend interviews expect it, and it's the area where \"it works for me\" answers fail most visibly.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"authentication","title":"Authentication","track":"Backend","covers":null,"summaryHtml":"Proving who a user is and deciding what they may do: sessions, tokens, OAuth 2.0 and OpenID Connect, passkeys, and authorization models. Full-stack interviews ask it constantly, and the follow-ups always land on where tokens live and how they're revoked.","summaryText":"Proving who a user is and deciding what they may do: sessions, tokens, OAuth 2.0 and OpenID Connect, passkeys, and authorization models. Full-stack interviews ask it constantly, and the follow-ups always land on where tokens live and how they're revoked.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"backend-patterns","title":"Backend patterns","track":"Backend","covers":null,"summaryHtml":"How a Node.js service is structured inside: frameworks and middleware, validation, error handling, layering, and the safeguards that keep it correct under load. Backend interviews probe these patterns through \"what happens when this request fails halfway\" questions.","summaryText":"How a Node.js service is structured inside: frameworks and middleware, validation, error handling, layering, and the safeguards that keep it correct under load. Backend interviews probe these patterns through \"what happens when this request fails halfway\" questions.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"browser","title":"Browser runtime","track":"Frontend","covers":null,"summaryHtml":"What the browser adds around the language: the DOM, events, the rendering pipeline, the HTML event loop, and Web APIs. Frontend interviews test this layer constantly — \"why is this click handler slow\" is a browser question, not a framework one.","summaryText":"What the browser adds around the language: the DOM, events, the rendering pipeline, the HTML event loop, and Web APIs. Frontend interviews test this layer constantly — \"why is this click handler slow\" is a browser question, not a framework one.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"caching","title":"Caching","track":"Backend","covers":null,"summaryHtml":"Caching on the server side of an API: in-process and Redis caches, cache patterns, invalidation, and HTTP caching for API responses. Interviews treat caching as a correctness question — stale data, stampedes, and invalidation are where answers fall apart.","summaryText":"Caching on the server side of an API: in-process and Redis caches, cache patterns, invalidation, and HTTP caching for API responses. Interviews treat caching as a correctness question — stale data, stampedes, and invalidation are where answers fall apart.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"ci-cd","title":"CI/CD","track":"Infrastructure and delivery","covers":null,"summaryHtml":"Getting a change from a commit to production safely: pipelines, deployment strategies, feature flags, mobile releases, and secrets. Interviews ask how you ship without breaking users, and how fast you can undo it when you do.","summaryText":"Getting a change from a commit to production safely: pipelines, deployment strategies, feature flags, mobile releases, and secrets. Interviews ask how you ship without breaking users, and how fast you can undo it when you do.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"cloud-and-iac","title":"Cloud and IaC","track":"Infrastructure and delivery","covers":null,"summaryHtml":"Running software on cloud platforms and describing that infrastructure as code: core services, serverless, the edge, and Terraform-style tooling. Interviews ask which building block fits a problem — and what it costs in latency, limits, and lock-in.","summaryText":"Running software on cloud platforms and describing that infrastructure as code: core services, serverless, the edge, and Terraform-style tooling. Interviews ask which building block fits a problem — and what it costs in latency, limits, and lock-in.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"containers-and-kubernetes","title":"Containers and Kubernetes","track":"Infrastructure and delivery","covers":null,"summaryHtml":"Packaging a service as a container image and running it on Kubernetes: images, isolation, scheduling, networking, and rollouts. Backend and platform interviews expect you to explain what a container really is and why a pod restarts.","summaryText":"Packaging a service as a container image and running it on Kubernetes: images, isolation, scheduling, networking, and rollouts. Backend and platform interviews expect you to explain what a container really is and why a pod restarts.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"data-structures-and-algorithms","title":"Data structures and algorithms","track":"Engineering practice","covers":null,"summaryHtml":"The data structures and algorithm patterns behind coding rounds, implemented and analysed in JavaScript. Coding interviews grade the reasoning — complexity, trade-offs, edge cases — as much as a working solution.","summaryText":"The data structures and algorithm patterns behind coding rounds, implemented and analysed in JavaScript. Coding interviews grade the reasoning — complexity, trade-offs, edge cases — as much as a working solution.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"databases","title":"Databases","track":"Backend","covers":null,"summaryHtml":"Storing and querying data correctly: relational modelling, indexes, transactions and isolation, NoSQL trade-offs, and data access from Node.js. Backend interviews use databases to test whether you can reason about correctness under concurrency, not just write a query.","summaryText":"Storing and querying data correctly: relational modelling, indexes, transactions and isolation, NoSQL trade-offs, and data access from Node.js. Backend interviews use databases to test whether you can reason about correctness under concurrency, not just write a query.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"git","title":"Git","track":"Infrastructure and delivery","covers":null,"summaryHtml":"How Git stores history and how teams work with it: the object model, branching and merging, rewriting history, and repository strategies. Interviews ask it through scenarios — a bad merge, a lost commit, a monorepo that's too slow — that only make sense once the model is clear.","summaryText":"How Git stores history and how teams work with it: the object model, branching and merging, rewriting history, and repository strategies. Interviews ask it through scenarios — a bad merge, a lost commit, a monorepo that's too slow — that only make sense once the model is clear.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"html-and-css","title":"HTML and CSS","track":"Frontend","covers":null,"summaryHtml":"Markup and styling as the platform defines them: semantic HTML, forms, the cascade, and layout. Interviews use them to separate engineers who understand layout from those who adjust values until it looks right.","summaryText":"Markup and styling as the platform defines them: semantic HTML, forms, the cascade, and layout. Interviews use them to separate engineers who understand layout from those who adjust values until it looks right.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"http-and-apis","title":"HTTP and APIs","track":"Backend","covers":null,"summaryHtml":"HTTP semantics and the API styles built on them: REST, GraphQL, gRPC, and real-time transports. Every backend and full-stack interview asks you to design or critique an API, and the answer rests on what HTTP actually guarantees.","summaryText":"HTTP semantics and the API styles built on them: REST, GraphQL, gRPC, and real-time transports. Every backend and full-stack interview asks you to design or critique an API, and the answer rests on what HTTP actually guarantees.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"javascript","title":"JavaScript","track":"Frontend","covers":"ECMAScript through ES2026, plus Stage 4 proposals shipping in ES2027; V8 as the reference engine.","summaryHtml":"The ECMAScript language, from values and types up to modules, memory, and the V8 engine. Frontend, backend, and full-stack interviews all test this layer — frameworks and runtimes are built on it.","summaryText":"The ECMAScript language, from values and types up to modules, memory, and the V8 engine. Frontend, backend, and full-stack interviews all test this layer — frameworks and runtimes are built on it.","flashcardCount":0,"chapterCount":26,"stats":{"total":150,"readable":0,"core":44,"byDifficulty":{"easy":36,"medium":89,"hard":25},"lastVerified":null,"stale":0,"reviewed":0,"drafted":150}},{"slug":"messaging-and-jobs","title":"Messaging and jobs","track":"Backend","covers":null,"summaryHtml":"Work that happens outside the request: queues, streams, background jobs, retries, and scheduling. Interviews use it to test whether you can keep work correct when messages arrive twice, late, or out of order.","summaryText":"Work that happens outside the request: queues, streams, background jobs, retries, and scheduling. Interviews use it to test whether you can keep work correct when messages arrive twice, late, or out of order.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"networking","title":"Networking","track":"Infrastructure and delivery","covers":null,"summaryHtml":"What happens between a URL and a response: DNS, TCP, TLS, HTTP/2 and HTTP/3, and the proxies and load balancers in the path. \"What happens when you type a URL\" is a classic interview opener, and every layer of it lives here.","summaryText":"What happens between a URL and a response: DNS, TCP, TLS, HTTP/2 and HTTP/3, and the proxies and load balancers in the path. \"What happens when you type a URL\" is a classic interview opener, and every layer of it lives here.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"nextjs","title":"Next.js","track":"Frontend","covers":null,"summaryHtml":"Next.js as a full-stack React framework: the App Router, rendering strategies, data fetching and caching, and deployment. Interviews for React roles increasingly assume it, and the hard questions are about where code runs and what gets cached.","summaryText":"Next.js as a full-stack React framework: the App Router, rendering strategies, data fetching and caching, and deployment. Interviews for React roles increasingly assume it, and the hard questions are about where code runs and what gets cached.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"nodejs","title":"Node.js runtime","track":"Backend","covers":null,"summaryHtml":"What Node.js adds around the language: libuv, its event-loop phases, the module systems, streams, and the process model. Backend and full-stack interviews probe this layer to see whether you know what actually blocks, what runs when, and why.","summaryText":"What Node.js adds around the language: libuv, its event-loop phases, the module systems, streams, and the process model. Backend and full-stack interviews probe this layer to see whether you know what actually blocks, what runs when, and why.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"observability","title":"Observability","track":"Infrastructure and delivery","covers":null,"summaryHtml":"Knowing what a running system is doing: logs, metrics, traces, alerting, SLOs, and responding when it breaks. Senior interviews ask how you'd find the cause of a production incident — and how you'd know about it before users do.","summaryText":"Knowing what a running system is doing: logs, metrics, traces, alerting, SLOs, and responding when it breaks. Senior interviews ask how you'd find the cause of a production incident — and how you'd know about it before users do.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"react","title":"React","track":"Frontend","covers":null,"summaryHtml":"React's rendering model, from components and hooks down to reconciliation, concurrent rendering, and Server Components. It's the most-asked frontend framework in interviews, and the hard questions are about when and why React renders.","summaryText":"React's rendering model, from components and hooks down to reconciliation, concurrent rendering, and Server Components. It's the most-asked frontend framework in interviews, and the hard questions are about when and why React renders.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"react-native","title":"React Native and Expo","track":"Frontend","covers":null,"summaryHtml":"How React renders to native iOS and Android views: the New Architecture, native modules, navigation, and shipping with Expo. Mobile interviews test whether you know where JavaScript ends and native begins — and what that costs in performance and releases.","summaryText":"How React renders to native iOS and Android views: the New Architecture, native modules, navigation, and shipping with Expo. Mobile interviews test whether you know where JavaScript ends and native begins — and what that costs in performance and releases.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"state-and-data-fetching","title":"State and data fetching","track":"Frontend","covers":null,"summaryHtml":"Where client state lives once it outgrows a component, and how server data is fetched, cached, and kept fresh on the client. Frontend interviews use it to separate people who reach for a library from people who can say what problem it solves.","summaryText":"Where client state lives once it outgrows a component, and how server data is fetched, cached, and kept fresh on the client. Frontend interviews use it to separate people who reach for a library from people who can say what problem it solves.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"system-design","title":"System design","track":"Engineering practice","covers":null,"summaryHtml":"Designing systems that scale and stay up: scalability, consistency, reliability patterns, and the classic design questions — backend and frontend. The system design round is often the one that decides seniority, and it rewards a method more than memorized diagrams.","summaryText":"Designing systems that scale and stay up: scalability, consistency, reliability patterns, and the classic design questions — backend and frontend. The system design round is often the one that decides seniority, and it rewards a method more than memorized diagrams.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"testing","title":"Testing","track":"Engineering practice","covers":null,"summaryHtml":"Testing JavaScript applications: what to test at which level, how test runners and mocks work, and how to keep tests trustworthy. Interviews use it to judge whether your code can be changed safely — by you or anyone else.","summaryText":"Testing JavaScript applications: what to test at which level, how test runners and mocks work, and how to keep tests trustworthy. Interviews use it to judge whether your code can be changed safely — by you or anyone else.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"tooling","title":"Tooling","track":"Engineering practice","covers":null,"summaryHtml":"The tools between source code and what ships: package managers, bundlers, transpilers, linters, and monorepos. Interviews ask about them when something breaks — a duplicate dependency, a bundle that won't tree-shake, a dual-package bug.","summaryText":"The tools between source code and what ships: package managers, bundlers, transpilers, linters, and monorepos. Interviews ask about them when something breaks — a duplicate dependency, a bundle that won't tree-shake, a dual-package bug.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"typescript","title":"TypeScript","track":"Frontend","covers":null,"summaryHtml":"TypeScript's type system and compiler: how types are checked, inferred, and erased. Most frontend and Node.js codebases are TypeScript now, and interviews probe whether you can reason about types rather than just annotate.","summaryText":"TypeScript's type system and compiler: how types are checked, inferred, and erased. Most frontend and Node.js codebases are TypeScript now, and interviews probe whether you can reason about types rather than just annotate.","flashcardCount":0,"chapterCount":8,"stats":{"total":47,"readable":0,"core":14,"byDifficulty":{"easy":3,"medium":30,"hard":14},"lastVerified":null,"stale":0,"reviewed":0,"drafted":47}},{"slug":"web-performance","title":"Web performance","track":"Engineering practice","covers":null,"summaryHtml":"Measuring and improving how fast pages load and respond: Core Web Vitals, the critical path, JavaScript cost, and the main thread. Interviews use it to test whether you can find a bottleneck with data instead of guessing.","summaryText":"Measuring and improving how fast pages load and respond: Core Web Vitals, the critical path, JavaScript cost, and the main thread. Interviews use it to test whether you can find a bottleneck with data instead of guessing.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}},{"slug":"web-security","title":"Web security","track":"Engineering practice","covers":null,"summaryHtml":"Security for web apps on both sides of the network: the browser's security model, common attacks, and the defences against them. Frontend and backend interviews both ask it, and the answers depend on knowing exactly what the browser enforces.","summaryText":"Security for web apps on both sides of the network: the browser's security model, common attacks, and the defences against them. Frontend and backend interviews both ask it, and the answers depend on knowing exactly what the browser enforces.","flashcardCount":0,"chapterCount":0,"stats":{"total":0,"readable":0,"core":0,"byDifficulty":{"easy":0,"medium":0,"hard":0},"lastVerified":null,"stale":0,"reviewed":0,"drafted":0}}],"paths":[{"slug":"frontend","title":"Frontend engineer","summary":"The language first, then the browser and frameworks, then performance, security and design.","steps":[{"topic":"javascript","topicTitle":"JavaScript","chapter":null,"chapterTitle":null,"why":"Every frontend interview starts at the language.","ready":false,"started":true,"questionCount":0},{"topic":"typescript","topicTitle":"TypeScript","chapter":null,"chapterTitle":null,"why":"Typed JavaScript is the default in most teams.","ready":false,"started":true,"questionCount":0},{"topic":"html-and-css","topicTitle":"HTML and CSS","chapter":null,"chapterTitle":null,"why":"Layout and semantics come up before any framework does.","ready":false,"started":false,"questionCount":0},{"topic":"browser","topicTitle":"Browser runtime","chapter":null,"chapterTitle":null,"why":"Rendering, events and storage explain most real bugs.","ready":false,"started":false,"questionCount":0},{"topic":"accessibility","topicTitle":"Accessibility","chapter":null,"chapterTitle":null,"why":"Expected of senior frontend work.","ready":false,"started":false,"questionCount":0},{"topic":"react","topicTitle":"React","chapter":null,"chapterTitle":null,"why":"The most-asked framework.","ready":false,"started":false,"questionCount":0},{"topic":"state-and-data-fetching","topicTitle":"State and data fetching","chapter":null,"chapterTitle":null,"why":"Where most frontend complexity lives.","ready":false,"started":false,"questionCount":0},{"topic":"nextjs","topicTitle":"Next.js","chapter":null,"chapterTitle":null,"why":"Server rendering and routing in practice.","ready":false,"started":false,"questionCount":0},{"topic":"web-performance","topicTitle":"Web performance","chapter":null,"chapterTitle":null,"why":"Measuring and fixing slow pages.","ready":false,"started":false,"questionCount":0},{"topic":"web-security","topicTitle":"Web security","chapter":null,"chapterTitle":null,"why":"XSS, CSP and the browser's trust model.","ready":false,"started":false,"questionCount":0},{"topic":"testing","topicTitle":"Testing","chapter":null,"chapterTitle":null,"why":"What to test and how.","ready":false,"started":false,"questionCount":0},{"topic":"system-design","topicTitle":"System design","chapter":null,"chapterTitle":null,"why":"Frontend design rounds at senior level.","ready":false,"started":false,"questionCount":0}],"start":null},{"slug":"backend","title":"Backend engineer","summary":"The language under Node.js, then HTTP, data, and the patterns that keep services reliable.","steps":[{"topic":"javascript","topicTitle":"JavaScript","chapter":null,"chapterTitle":null,"why":"The language under Node.js.","ready":false,"started":true,"questionCount":0},{"topic":"nodejs","topicTitle":"Node.js runtime","chapter":null,"chapterTitle":null,"why":"The runtime, its event loop and its modules.","ready":false,"started":false,"questionCount":0},{"topic":"http-and-apis","topicTitle":"HTTP and APIs","chapter":null,"chapterTitle":null,"why":"Every service speaks HTTP.","ready":false,"started":false,"questionCount":0},{"topic":"databases","topicTitle":"Databases","chapter":null,"chapterTitle":null,"why":"Modelling, queries and transactions.","ready":false,"started":false,"questionCount":0},{"topic":"caching","topicTitle":"Caching","chapter":null,"chapterTitle":null,"why":"Speed and its consistency costs.","ready":false,"started":false,"questionCount":0},{"topic":"backend-patterns","topicTitle":"Backend patterns","chapter":null,"chapterTitle":null,"why":"Structuring services that last.","ready":false,"started":false,"questionCount":0},{"topic":"messaging-and-jobs","topicTitle":"Messaging and jobs","chapter":null,"chapterTitle":null,"why":"Work that should not block a request.","ready":false,"started":false,"questionCount":0},{"topic":"authentication","topicTitle":"Authentication","chapter":null,"chapterTitle":null,"why":"Sessions, tokens and getting them right.","ready":false,"started":false,"questionCount":0},{"topic":"observability","topicTitle":"Observability","chapter":null,"chapterTitle":null,"why":"Knowing what production is doing.","ready":false,"started":false,"questionCount":0},{"topic":"web-security","topicTitle":"Web security","chapter":null,"chapterTitle":null,"why":"Attacks a backend must expect.","ready":false,"started":false,"questionCount":0},{"topic":"testing","topicTitle":"Testing","chapter":null,"chapterTitle":null,"why":"Confidence without slow suites.","ready":false,"started":false,"questionCount":0},{"topic":"system-design","topicTitle":"System design","chapter":null,"chapterTitle":null,"why":"The senior backend round.","ready":false,"started":false,"questionCount":0}],"start":null},{"slug":"full-stack","title":"Full-stack engineer","summary":"The language first, then both sides of the wire, then the questions that span them.","steps":[{"topic":"javascript","topicTitle":"JavaScript","chapter":null,"chapterTitle":null,"why":"One language across the stack.","ready":false,"started":true,"questionCount":0},{"topic":"typescript","topicTitle":"TypeScript","chapter":null,"chapterTitle":null,"why":"Shared types between client and server.","ready":false,"started":true,"questionCount":0},{"topic":"html-and-css","topicTitle":"HTML and CSS","chapter":null,"chapterTitle":null,"why":"The client's foundation.","ready":false,"started":false,"questionCount":0},{"topic":"react","topicTitle":"React","chapter":null,"chapterTitle":null,"why":"The most common client framework.","ready":false,"started":false,"questionCount":0},{"topic":"nodejs","topicTitle":"Node.js runtime","chapter":null,"chapterTitle":null,"why":"The most common server runtime for JavaScript teams.","ready":false,"started":false,"questionCount":0},{"topic":"http-and-apis","topicTitle":"HTTP and APIs","chapter":null,"chapterTitle":null,"why":"The contract between the two sides.","ready":false,"started":false,"questionCount":0},{"topic":"databases","topicTitle":"Databases","chapter":null,"chapterTitle":null,"why":"Where the data lives.","ready":false,"started":false,"questionCount":0},{"topic":"authentication","topicTitle":"Authentication","chapter":null,"chapterTitle":null,"why":"Crosses client and server.","ready":false,"started":false,"questionCount":0},{"topic":"nextjs","topicTitle":"Next.js","chapter":null,"chapterTitle":null,"why":"Where the two sides meet in one framework.","ready":false,"started":false,"questionCount":0},{"topic":"web-security","topicTitle":"Web security","chapter":null,"chapterTitle":null,"why":"Attacks on both sides.","ready":false,"started":false,"questionCount":0},{"topic":"testing","topicTitle":"Testing","chapter":null,"chapterTitle":null,"why":"Tests at each layer.","ready":false,"started":false,"questionCount":0},{"topic":"system-design","topicTitle":"System design","chapter":null,"chapterTitle":null,"why":"End-to-end design rounds.","ready":false,"started":false,"questionCount":0}],"start":null},{"slug":"infrastructure-and-devops","title":"Infrastructure and DevOps","summary":"Version control and networks first, then containers, delivery pipelines and the cloud.","steps":[{"topic":"git","topicTitle":"Git","chapter":null,"chapterTitle":null,"why":"The base of every delivery pipeline.","ready":false,"started":false,"questionCount":0},{"topic":"networking","topicTitle":"Networking","chapter":null,"chapterTitle":null,"why":"DNS, TCP and TLS explain most outages.","ready":false,"started":false,"questionCount":0},{"topic":"containers-and-kubernetes","topicTitle":"Containers and Kubernetes","chapter":null,"chapterTitle":null,"why":"How software is packaged and run.","ready":false,"started":false,"questionCount":0},{"topic":"ci-cd","topicTitle":"CI/CD","chapter":null,"chapterTitle":null,"why":"Getting changes to production safely.","ready":false,"started":false,"questionCount":0},{"topic":"cloud-and-iac","topicTitle":"Cloud and IaC","chapter":null,"chapterTitle":null,"why":"Infrastructure as reviewed code.","ready":false,"started":false,"questionCount":0},{"topic":"observability","topicTitle":"Observability","chapter":null,"chapterTitle":null,"why":"Metrics, logs and traces.","ready":false,"started":false,"questionCount":0},{"topic":"web-security","topicTitle":"Web security","chapter":null,"chapterTitle":null,"why":"Securing what you deploy.","ready":false,"started":false,"questionCount":0},{"topic":"system-design","topicTitle":"System design","chapter":null,"chapterTitle":null,"why":"Designing for failure.","ready":false,"started":false,"questionCount":0}],"start":null},{"slug":"any-engineer","title":"Any engineer","summary":"The topics asked of every software engineer, whatever the stack.","steps":[{"topic":"data-structures-and-algorithms","topicTitle":"Data structures and algorithms","chapter":null,"chapterTitle":null,"why":"The shared vocabulary of coding rounds.","ready":false,"started":false,"questionCount":0},{"topic":"git","topicTitle":"Git","chapter":null,"chapterTitle":null,"why":"Daily tooling every team assumes.","ready":false,"started":false,"questionCount":0},{"topic":"networking","topicTitle":"Networking","chapter":null,"chapterTitle":null,"why":"What happens between two machines.","ready":false,"started":false,"questionCount":0},{"topic":"http-and-apis","topicTitle":"HTTP and APIs","chapter":null,"chapterTitle":null,"why":"How services talk.","ready":false,"started":false,"questionCount":0},{"topic":"databases","topicTitle":"Databases","chapter":null,"chapterTitle":null,"why":"Storing and querying data.","ready":false,"started":false,"questionCount":0},{"topic":"testing","topicTitle":"Testing","chapter":null,"chapterTitle":null,"why":"Shipping with confidence.","ready":false,"started":false,"questionCount":0},{"topic":"web-security","topicTitle":"Web security","chapter":null,"chapterTitle":null,"why":"Common attacks and defences.","ready":false,"started":false,"questionCount":0},{"topic":"system-design","topicTitle":"System design","chapter":null,"chapterTitle":null,"why":"Putting the pieces together.","ready":false,"started":false,"questionCount":0}],"start":null}]},"topic":{"slug":"javascript","title":"JavaScript","track":"Frontend","covers":"ECMAScript through ES2026, plus Stage 4 proposals shipping in ES2027; V8 as the reference engine.","summaryHtml":"The ECMAScript language, from values and types up to modules, memory, and the V8 engine. Frontend, backend, and full-stack interviews all test this layer — frameworks and runtimes are built on it.","summaryText":"The ECMAScript language, from values and types up to modules, memory, and the V8 engine. Frontend, backend, and full-stack interviews all test this layer — frameworks and runtimes are built on it.","flashcardCount":0,"chapters":[{"number":"01","slug":"how-javascript-runs","title":"How JavaScript runs","summaryHtml":"What JavaScript is made of — the specification, engines, and hosts — how features get added, and the two kinds of source code it runs.","summaryText":"What JavaScript is made of — the specification, engines, and hosts — how features get added, and the two kinds of source code it runs.","questions":[{"id":"javascript/how-javascript-runs/ecmascript-engine-host","number":"010","title":"What's the difference between ECMAScript, JavaScript, an engine, and a host?","titleHtml":"What's the difference between ECMAScript, JavaScript, an engine, and a host?","status":"draft","difficulty":"easy","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/how-javascript-runs/tc39-process","number":"020","title":"How does a feature become part of JavaScript?","titleHtml":"How does a feature become part of JavaScript?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/how-javascript-runs/compiled-or-interpreted","number":"030","title":"Is JavaScript compiled or interpreted?","titleHtml":"Is JavaScript compiled or interpreted?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/how-javascript-runs/scripts-vs-modules","number":"040","title":"What's the difference between a script and a module?","titleHtml":"What's the difference between a script and a module?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/how-javascript-runs/strict-mode","number":"050","title":"What does strict mode change, and when is code strict automatically?","titleHtml":"What does strict mode change, and when is code strict automatically?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/how-javascript-runs/polyfill-vs-transpiler","number":"060","title":"What's the difference between a polyfill and a transpiler?","titleHtml":"What's the difference between a polyfill and a transpiler?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"02","slug":"values-and-types","title":"Values and types","summaryHtml":"The eight language types, how primitives differ from objects, and how to check what a value is.","summaryText":"The eight language types, how primitives differ from objects, and how to check what a value is.","questions":[{"id":"javascript/values-and-types/language-types","number":"010","title":"What are JavaScript's types?","titleHtml":"What are JavaScript's types?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/values-and-types/typeof-null","number":"020","title":"Why does typeof null return \"object\"?","titleHtml":"Why does typeof null return \"object\"?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/values-and-types/null-vs-undefined","number":"030","title":"What's the difference between null and undefined?","titleHtml":"What's the difference between null and undefined?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/values-and-types/primitive-wrappers","number":"040","title":"How can a primitive have methods?","titleHtml":"How can a primitive have methods?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/values-and-types/pass-by-sharing","number":"050","title":"Is JavaScript pass-by-value or pass-by-reference?","titleHtml":"Is JavaScript pass-by-value or pass-by-reference?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/values-and-types/symbols","number":"060","title":"What are Symbols for?","titleHtml":"What are Symbols for?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/values-and-types/type-checking","number":"070","title":"How do you reliably check a value's type?","titleHtml":"How do you reliably check a value's type?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"03","slug":"numbers-and-bigint","title":"Numbers and BigInt","summaryHtml":"How JavaScript numbers work as IEEE 754 doubles, their special values, and when BigInt takes over.","summaryText":"How JavaScript numbers work as IEEE 754 doubles, their special values, and when BigInt takes over.","questions":[{"id":"javascript/numbers-and-bigint/floating-point-precision","number":"010","title":"Why is 0.1 + 0.2 !== 0.3?","titleHtml":"Why is 0.1 + 0.2 !== 0.3?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/numbers-and-bigint/nan-negative-zero-infinity","number":"020","title":"What are NaN, -0, and Infinity, and how do you test for them?","titleHtml":"What are NaN, -0, and Infinity, and how do you test for them?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/numbers-and-bigint/safe-integers-bigint","number":"030","title":"What's Number.MAX_SAFE_INTEGER, and when do you need BigInt?","titleHtml":"What's Number.MAX_SAFE_INTEGER, and when do you need BigInt?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/numbers-and-bigint/parsing-numbers","number":"040","title":"Number() vs parseInt() vs unary + — how do they differ?","titleHtml":"Number() vs parseInt() vs unary + — how do they differ?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/numbers-and-bigint/math-sumprecise","number":"050","title":"How do you sum floating-point numbers accurately?","titleHtml":"How do you sum floating-point numbers accurately?","status":"draft","difficulty":"medium","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"04","slug":"strings-and-unicode","title":"Strings and Unicode","summaryHtml":"Strings as UTF-16 code units, what that means for length and iteration, and template literals.","summaryText":"Strings as UTF-16 code units, what that means for length and iteration, and template literals.","questions":[{"id":"javascript/strings-and-unicode/utf16-string-length","number":"010","title":"Why is \"😀\".length 2?","titleHtml":"Why is \"😀\".length 2?","status":"draft","difficulty":"medium","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/strings-and-unicode/graphemes-and-code-points","number":"020","title":"How do you iterate over the characters a user sees?","titleHtml":"How do you iterate over the characters a user sees?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/strings-and-unicode/well-formed-strings","number":"030","title":"What are lone surrogates, and what do isWellFormed and toWellFormed fix?","titleHtml":"What are lone surrogates, and what do isWellFormed and toWellFormed fix?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/strings-and-unicode/tagged-templates","number":"040","title":"How do tagged template literals work?","titleHtml":"How do tagged template literals work?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/strings-and-unicode/locale-comparison-normalization","number":"050","title":"How do you compare strings correctly across languages?","titleHtml":"How do you compare strings correctly across languages?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"05","slug":"coercion-and-equality","title":"Coercion and equality","summaryHtml":"How values convert between types, the algorithms behind == and ===, and which comparison each API uses.","summaryText":"How values convert between types, the algorithms behind == and ===, and which comparison each API uses.","questions":[{"id":"javascript/coercion-and-equality/loose-equality","number":"010","title":"How does == decide whether two values are equal?","titleHtml":"How does == decide whether two values are equal?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/coercion-and-equality/truthy-falsy","number":"020","title":"Which values are falsy?","titleHtml":"Which values are falsy?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/coercion-and-equality/object-to-primitive","number":"030","title":"How does an object convert to a primitive?","titleHtml":"How does an object convert to a primitive?","status":"draft","difficulty":"hard","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/coercion-and-equality/addition-operator-coercion","number":"040","title":"Why does [] + {} give \"[object Object]\"?","titleHtml":"Why does [] + {} give \"[object Object]\"?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/coercion-and-equality/equality-algorithms","number":"050","title":"=== vs Object.is vs SameValueZero — which comparison does each API use?","titleHtml":"=== vs Object.is vs SameValueZero — which comparison does each API use?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"06","slug":"operators-and-syntax","title":"Operators and syntax","summaryHtml":"Everyday syntax interviewers probe: destructuring, spread and rest, short-circuiting operators, loops, and semicolons.","summaryText":"Everyday syntax interviewers probe: destructuring, spread and rest, short-circuiting operators, loops, and semicolons.","questions":[{"id":"javascript/operators-and-syntax/destructuring","number":"010","title":"How does destructuring work, and where does it throw?","titleHtml":"How does destructuring work, and where does it throw?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/operators-and-syntax/spread-vs-rest","number":"020","title":"What's the difference between spread and rest?","titleHtml":"What's the difference between spread and rest?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/operators-and-syntax/nullish-and-optional-chaining","number":"030","title":"?? vs ||, and how do optional chaining and logical assignment short-circuit?","titleHtml":"?? vs ||, and how do optional chaining and logical assignment short-circuit?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/operators-and-syntax/loop-statements","number":"040","title":"for…in vs for…of vs forEach — when do you use each?","titleHtml":"for…in vs for…of vs forEach — when do you use each?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/operators-and-syntax/automatic-semicolon-insertion","number":"050","title":"How does automatic semicolon insertion work, and when does it bite?","titleHtml":"How does automatic semicolon insertion work, and when does it bite?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"07","slug":"scope-and-execution-contexts","title":"Scope, hoisting, and execution contexts","summaryHtml":"How bindings are created and found: scope, hoisting, the TDZ, and the spec machinery underneath — execution contexts, Environment Records, and realms.","summaryText":"How bindings are created and found: scope, hoisting, the TDZ, and the spec machinery underneath — execution contexts, Environment Records, and realms.","questions":[{"id":"javascript/scope-and-execution-contexts/var-let-const","number":"010","title":"What's the difference between var, let, and const?","titleHtml":"What's the difference between var, let, and const?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/hoisting","number":"020","title":"What is hoisting, really?","titleHtml":"What is hoisting, really?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/temporal-dead-zone","number":"030","title":"What is the temporal dead zone?","titleHtml":"What is the temporal dead zone?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/lexical-scope-chain","number":"040","title":"What is lexical scope, and how does the scope chain work?","titleHtml":"What is lexical scope, and how does the scope chain work?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/execution-context-call-stack","number":"050","title":"What is an execution context, and what does the call stack hold?","titleHtml":"What is an execution context, and what does the call stack hold?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/environment-records","number":"060","title":"What is an Environment Record?","titleHtml":"What is an Environment Record?","status":"draft","difficulty":"hard","frequency":1,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/global-object-globalthis","number":"070","title":"What is the global object, and how does globalThis relate to global variables?","titleHtml":"What is the global object, and how does globalThis relate to global variables?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/stack-overflow-tail-calls","number":"080","title":"What causes \"Maximum call stack size exceeded\", and do tail calls help?","titleHtml":"What causes \"Maximum call stack size exceeded\", and do tail calls help?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/scope-and-execution-contexts/realms","number":"090","title":"What is a realm, and why does instanceof Array fail across iframes?","titleHtml":"What is a realm, and why does instanceof Array fail across iframes?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"08","slug":"functions","title":"Functions","summaryHtml":"The function forms and how they differ, parameters, and the functional techniques interviews ask you to implement.","summaryText":"The function forms and how they differ, parameters, and the functional techniques interviews ask you to implement.","questions":[{"id":"javascript/functions/function-forms","number":"010","title":"Function declarations vs expressions vs arrow functions — what actually differs?","titleHtml":"Function declarations vs expressions vs arrow functions — what actually differs?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/functions/default-and-rest-parameters","number":"020","title":"How do default and rest parameters work?","titleHtml":"How do default and rest parameters work?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/functions/arguments-object","number":"030","title":"What is the arguments object, and why avoid it?","titleHtml":"What is the arguments object, and why avoid it?","status":"draft","difficulty":"easy","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/functions/higher-order-functions","number":"040","title":"What are higher-order functions?","titleHtml":"What are higher-order functions?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/functions/iife","number":"050","title":"What is an IIFE, and do you still need one?","titleHtml":"What is an IIFE, and do you still need one?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/functions/currying-partial-application","number":"060","title":"What are currying and partial application?","titleHtml":"What are currying and partial application?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/functions/compose-and-pipe","number":"070","title":"Implement compose and pipe.","titleHtml":"Implement compose and pipe.","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"09","slug":"closures","title":"Closures","summaryHtml":"What a closure is in terms of environments, what it keeps alive, and the patterns built on it.","summaryText":"What a closure is in terms of environments, what it keeps alive, and the patterns built on it.","questions":[{"id":"javascript/closures/what-is-a-closure","number":"010","title":"What is a closure?","titleHtml":"What is a closure?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/closures/closures-in-loops","number":"020","title":"Why does a for (var i…) loop with setTimeout print the same number?","titleHtml":"Why does a for (var i…) loop with setTimeout print the same number?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/closures/closure-memory","number":"030","title":"What does a closure keep alive in memory?","titleHtml":"What does a closure keep alive in memory?","status":"draft","difficulty":"hard","frequency":2,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/closures/private-state","number":"040","title":"How do closures create private state?","titleHtml":"How do closures create private state?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/closures/debounce-throttle-once","number":"050","title":"Implement debounce, throttle, and once.","titleHtml":"Implement debounce, throttle, and once.","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"10","slug":"this","title":"`this`","summaryHtml":"How this is bound at each call site, why arrows differ, and how to control it.","summaryText":"How this is bound at each call site, why arrows differ, and how to control it.","questions":[{"id":"javascript/this/this-binding-rules","number":"010","title":"How is the value of this determined?","titleHtml":"How is the value of this determined?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/this/arrow-functions-this","number":"020","title":"Why don't arrow functions have their own this?","titleHtml":"Why don't arrow functions have their own this?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/this/call-apply-bind","number":"030","title":"call vs apply vs bind?","titleHtml":"call vs apply vs bind?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/this/lost-this-callbacks","number":"040","title":"Why does a method lose this when passed as a callback?","titleHtml":"Why does a method lose this when passed as a callback?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/this/implement-bind","number":"050","title":"Implement Function.prototype.bind.","titleHtml":"Implement Function.prototype.bind.","status":"draft","difficulty":"hard","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"11","slug":"objects-and-properties","title":"Objects and properties","summaryHtml":"The property model — keys, attributes, accessors, integrity levels — and copying and comparing objects.","summaryText":"The property model — keys, attributes, accessors, integrity levels — and copying and comparing objects.","questions":[{"id":"javascript/objects-and-properties/property-keys-and-order","number":"010","title":"What can be a property key, and in what order are keys listed?","titleHtml":"What can be a property key, and in what order are keys listed?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/objects-and-properties/property-descriptors","number":"020","title":"What are property descriptors?","titleHtml":"What are property descriptors?","status":"draft","difficulty":"medium","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/objects-and-properties/freeze-seal-preventextensions","number":"030","title":"Object.freeze vs seal vs preventExtensions?","titleHtml":"Object.freeze vs seal vs preventExtensions?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/objects-and-properties/getters-and-setters","number":"040","title":"How do getters and setters work?","titleHtml":"How do getters and setters work?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/objects-and-properties/enumerating-properties","number":"050","title":"How do you list an object's properties?","titleHtml":"How do you list an object's properties?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/objects-and-properties/shallow-vs-deep-copy","number":"060","title":"Shallow vs deep copy — spread, Object.assign, or structuredClone?","titleHtml":"Shallow vs deep copy — spread, Object.assign, or structuredClone?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/objects-and-properties/deep-equality","number":"070","title":"How do you compare two objects for equality?","titleHtml":"How do you compare two objects for equality?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"12","slug":"prototypes","title":"Prototypes and inheritance","summaryHtml":"The [[Prototype]] chain, how lookup and assignment walk it, and what new and instanceof do.","summaryText":"The [[Prototype]] chain, how lookup and assignment walk it, and what new and instanceof do.","questions":[{"id":"javascript/prototypes/prototype-chain","number":"010","title":"How does prototypal inheritance work?","titleHtml":"How does prototypal inheritance work?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/prototypes/proto-vs-prototype","number":"020","title":"__proto__ vs prototype vs Object.getPrototypeOf?","titleHtml":"__proto__ vs prototype vs Object.getPrototypeOf?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/prototypes/new-operator","number":"030","title":"What does the new operator do?","titleHtml":"What does the new operator do?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/prototypes/instanceof","number":"040","title":"How does instanceof work?","titleHtml":"How does instanceof work?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/prototypes/object-create-null","number":"050","title":"When do you use Object.create(null)?","titleHtml":"When do you use Object.create(null)?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/prototypes/extending-native-prototypes","number":"060","title":"Should you extend native prototypes?","titleHtml":"Should you extend native prototypes?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"13","slug":"classes","title":"Classes","summaryHtml":"What class adds over constructor functions: fields, private names, static blocks, super, and subclassing built-ins.","summaryText":"What class adds over constructor functions: fields, private names, static blocks, super, and subclassing built-ins.","questions":[{"id":"javascript/classes/classes-vs-prototypes","number":"010","title":"Are classes just syntactic sugar over prototypes?","titleHtml":"Are classes just syntactic sugar over prototypes?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/classes/private-fields","number":"020","title":"How do private fields (#x) work?","titleHtml":"How do private fields (#x) work?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/classes/fields-vs-methods","number":"030","title":"Class fields vs methods — where does each live?","titleHtml":"Class fields vs methods — where does each live?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/classes/static-members-and-blocks","number":"040","title":"What are static members and static initialization blocks?","titleHtml":"What are static members and static initialization blocks?","status":"draft","difficulty":"easy","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/classes/super-keyword","number":"050","title":"How does super work?","titleHtml":"How does super work?","status":"draft","difficulty":"hard","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/classes/extending-built-ins","number":"060","title":"How do you extend built-ins like Array and Error?","titleHtml":"How do you extend built-ins like Array and Error?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/classes/composition-vs-inheritance","number":"070","title":"Composition vs inheritance — when do mixins make sense?","titleHtml":"Composition vs inheritance — when do mixins make sense?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"14","slug":"arrays","title":"Arrays","summaryHtml":"Array semantics and methods — mutating vs copying, sorting, holes, searching — and the polyfills interviewers ask for.","summaryText":"Array semantics and methods — mutating vs copying, sorting, holes, searching — and the polyfills interviewers ask for.","questions":[{"id":"javascript/arrays/mutating-vs-copying-methods","number":"010","title":"Which array methods mutate, and what are their copying versions?","titleHtml":"Which array methods mutate, and what are their copying versions?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/arrays/array-sort","number":"020","title":"How does Array.prototype.sort work?","titleHtml":"How does Array.prototype.sort work?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/arrays/implement-map-filter-reduce","number":"030","title":"Implement map, filter, and reduce.","titleHtml":"Implement map, filter, and reduce.","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/arrays/sparse-arrays","number":"040","title":"What are sparse arrays and holes?","titleHtml":"What are sparse arrays and holes?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/arrays/array-from-and-fromasync","number":"050","title":"Array-likes vs iterables: how do Array.from and Array.fromAsync work?","titleHtml":"Array-likes vs iterables: how do Array.from and Array.fromAsync work?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/arrays/searching-arrays","number":"060","title":"includes vs indexOf vs find vs findLast vs at?","titleHtml":"includes vs indexOf vs find vs findLast vs at?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/arrays/flat-and-flatmap","number":"070","title":"How do flat and flatMap work?","titleHtml":"How do flat and flatMap work?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"15","slug":"keyed-collections","title":"Keyed collections","summaryHtml":"Map, Set, and their weak variants, plus grouping and upsert helpers.","summaryText":"Map, Set, and their weak variants, plus grouping and upsert helpers.","questions":[{"id":"javascript/keyed-collections/map-vs-object","number":"010","title":"When do you use a Map instead of an object?","titleHtml":"When do you use a Map instead of an object?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/keyed-collections/set-methods","number":"020","title":"What can a Set do in ES2025?","titleHtml":"What can a Set do in ES2025?","status":"draft","difficulty":"easy","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/keyed-collections/weakmap-weakset","number":"030","title":"What are WeakMap and WeakSet for, and why can't you iterate them?","titleHtml":"What are WeakMap and WeakSet for, and why can't you iterate them?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/keyed-collections/groupby","number":"040","title":"How do Object.groupBy and Map.groupBy work?","titleHtml":"How do Object.groupBy and Map.groupBy work?","status":"draft","difficulty":"easy","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/keyed-collections/map-upsert","number":"050","title":"What does Map.prototype.getOrInsert solve?","titleHtml":"What does Map.prototype.getOrInsert solve?","status":"draft","difficulty":"easy","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"16","slug":"iterators-and-generators","title":"Iterators and generators","summaryHtml":"The iteration protocols, generators as pausable functions, lazy iterator helpers, and async iteration.","summaryText":"The iteration protocols, generators as pausable functions, lazy iterator helpers, and async iteration.","questions":[{"id":"javascript/iterators-and-generators/iteration-protocols","number":"010","title":"What are the iteration protocols?","titleHtml":"What are the iteration protocols?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/iterators-and-generators/generators","number":"020","title":"How do generators pause and resume?","titleHtml":"How do generators pause and resume?","status":"draft","difficulty":"hard","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/iterators-and-generators/iterator-helpers","number":"030","title":"What are iterator helpers, and why are they lazy?","titleHtml":"What are iterator helpers, and why are they lazy?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/iterators-and-generators/new-iterator-methods","number":"040","title":"What's new for iterators after ES2025?","titleHtml":"What's new for iterators after ES2025?","status":"draft","difficulty":"medium","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/iterators-and-generators/async-iteration","number":"050","title":"How do async iterators and for await…of work?","titleHtml":"How do async iterators and for await…of work?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"17","slug":"promises","title":"Promises","summaryHtml":"Promise states and resolution, chaining, combinators, error propagation, and implementing promises yourself.","summaryText":"Promise states and resolution, chaining, combinators, error propagation, and implementing promises yourself.","questions":[{"id":"javascript/promises/what-is-a-promise","number":"010","title":"What is a Promise?","titleHtml":"What is a Promise?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/promise-chaining","number":"020","title":"How does promise chaining work?","titleHtml":"How does promise chaining work?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/promise-combinators","number":"030","title":"Promise.all vs allSettled vs race vs any?","titleHtml":"Promise.all vs allSettled vs race vs any?","status":"draft","difficulty":"easy","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/promise-error-handling","number":"040","title":"How do errors propagate through promises, and what is an unhandled rejection?","titleHtml":"How do errors propagate through promises, and what is an unhandled rejection?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/withresolvers-and-try","number":"050","title":"What do Promise.withResolvers and Promise.try solve?","titleHtml":"What do Promise.withResolvers and Promise.try solve?","status":"draft","difficulty":"medium","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/implement-promise-all","number":"060","title":"Implement Promise.all.","titleHtml":"Implement Promise.all.","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/implement-a-promise","number":"070","title":"Implement a Promise from scratch.","titleHtml":"Implement a Promise from scratch.","status":"draft","difficulty":"hard","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/promises/promisify","number":"080","title":"How do you convert a callback API to promises?","titleHtml":"How do you convert a callback API to promises?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"18","slug":"async-and-the-event-loop","title":"Async functions and the event loop","summaryHtml":"How JavaScript schedules work — jobs, tasks, and microtasks — how async/await maps onto promises, and how to run and cancel async work well.","summaryText":"How JavaScript schedules work — jobs, tasks, and microtasks — how async/await maps onto promises, and how to run and cancel async work well.","questions":[{"id":"javascript/async-and-the-event-loop/event-loop","number":"010","title":"How does the event loop work?","titleHtml":"How does the event loop work?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/async-and-the-event-loop/task-microtask-ordering","number":"020","title":"Predict the order: setTimeout vs promises vs queueMicrotask.","titleHtml":"Predict the order: setTimeout vs promises vs queueMicrotask.","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/async-and-the-event-loop/async-await-mechanics","number":"030","title":"How does async/await work under the hood?","titleHtml":"How does async/await work under the hood?","status":"draft","difficulty":"hard","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/async-and-the-event-loop/sequential-vs-parallel-await","number":"040","title":"Sequential vs parallel await — and await inside loops?","titleHtml":"Sequential vs parallel await — and await inside loops?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/async-and-the-event-loop/single-threaded","number":"050","title":"Is JavaScript single-threaded?","titleHtml":"Is JavaScript single-threaded?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/async-and-the-event-loop/cancelling-async-work","number":"060","title":"How do you cancel async work?","titleHtml":"How do you cancel async work?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/async-and-the-event-loop/concurrency-limit-retry","number":"070","title":"Implement a concurrency-limited task runner with retry.","titleHtml":"Implement a concurrency-limited task runner with retry.","status":"draft","difficulty":"hard","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"19","slug":"errors-and-cleanup","title":"Errors and cleanup","summaryHtml":"Throwing, catching, and custom errors; why async errors escape try; and deterministic cleanup with using.","summaryText":"Throwing, catching, and custom errors; why async errors escape try; and deterministic cleanup with using.","questions":[{"id":"javascript/errors-and-cleanup/try-catch-finally","number":"010","title":"How do try, catch, and finally interact with return?","titleHtml":"How do try, catch, and finally interact with return?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/errors-and-cleanup/custom-errors","number":"020","title":"How do you create custom errors?","titleHtml":"How do you create custom errors?","status":"draft","difficulty":"easy","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/errors-and-cleanup/async-error-boundaries","number":"030","title":"Why doesn't try/catch catch errors in a callback?","titleHtml":"Why doesn't try/catch catch errors in a callback?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/errors-and-cleanup/explicit-resource-management","number":"040","title":"What do using and await using do?","titleHtml":"What do using and await using do?","status":"draft","difficulty":"medium","frequency":1,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/errors-and-cleanup/uncaught-errors","number":"050","title":"How do you handle errors you didn't catch?","titleHtml":"How do you handle errors you didn't catch?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"20","slug":"modules","title":"Modules","summaryHtml":"How ES modules load and link, how they differ from CommonJS, and the newer module features.","summaryText":"How ES modules load and link, how they differ from CommonJS, and the newer module features.","questions":[{"id":"javascript/modules/es-module-loading","number":"010","title":"How do ES modules load?","titleHtml":"How do ES modules load?","status":"draft","difficulty":"hard","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/modules/esm-vs-commonjs","number":"020","title":"ES modules vs CommonJS — what differs and how do they interoperate?","titleHtml":"ES modules vs CommonJS — what differs and how do they interoperate?","status":"draft","difficulty":"medium","frequency":5,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/modules/circular-imports","number":"030","title":"What happens with circular imports?","titleHtml":"What happens with circular imports?","status":"draft","difficulty":"hard","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/modules/dynamic-import","number":"040","title":"How does dynamic import() work?","titleHtml":"How does dynamic import() work?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/modules/top-level-await","number":"050","title":"What does top-level await do to the module graph?","titleHtml":"What does top-level await do to the module graph?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/modules/import-attributes-json-modules","number":"060","title":"What are import attributes and JSON modules?","titleHtml":"What are import attributes and JSON modules?","status":"draft","difficulty":"easy","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/modules/import-meta","number":"070","title":"What is import.meta?","titleHtml":"What is import.meta?","status":"draft","difficulty":"easy","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"21","slug":"metaprogramming","title":"Metaprogramming","summaryHtml":"Intercepting and customizing language behaviour: Proxy, Reflect, well-known symbols, exotic objects, and eval.","summaryText":"Intercepting and customizing language behaviour: Proxy, Reflect, well-known symbols, exotic objects, and eval.","questions":[{"id":"javascript/metaprogramming/proxy-traps-invariants","number":"010","title":"What can a Proxy intercept, and what are its invariants?","titleHtml":"What can a Proxy intercept, and what are its invariants?","status":"draft","difficulty":"hard","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/metaprogramming/reflect-api","number":"020","title":"What is Reflect for?","titleHtml":"What is Reflect for?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/metaprogramming/well-known-symbols","number":"030","title":"Which well-known symbols let you customize built-in behavior?","titleHtml":"Which well-known symbols let you customize built-in behavior?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/metaprogramming/exotic-objects","number":"040","title":"What is an exotic object?","titleHtml":"What is an exotic object?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/metaprogramming/eval-direct-indirect","number":"050","title":"Why is eval dangerous, and what's the difference between direct and indirect eval?","titleHtml":"Why is eval dangerous, and what's the difference between direct and indirect eval?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"22","slug":"regular-expressions","title":"Regular expressions","summaryHtml":"Regex flags, groups and lookarounds, performance traps, and the APIs that use patterns.","summaryText":"Regex flags, groups and lookarounds, performance traps, and the APIs that use patterns.","questions":[{"id":"javascript/regular-expressions/regex-flags","number":"010","title":"What do the regex flags do?","titleHtml":"What do the regex flags do?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/regular-expressions/named-groups-lookbehind","number":"020","title":"How do named groups and lookbehind work?","titleHtml":"How do named groups and lookbehind work?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/regular-expressions/catastrophic-backtracking","number":"030","title":"What is catastrophic backtracking?","titleHtml":"What is catastrophic backtracking?","status":"draft","difficulty":"hard","frequency":2,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/regular-expressions/regex-methods","number":"040","title":"match vs matchAll vs exec vs replace — and RegExp.escape?","titleHtml":"match vs matchAll vs exec vs replace — and RegExp.escape?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"23","slug":"dates-temporal-intl","title":"Dates, Temporal, and Intl","summaryHtml":"Why Date is error-prone, how Temporal replaces it, and locale-aware formatting with Intl.","summaryText":"Why Date is error-prone, how Temporal replaces it, and locale-aware formatting with Intl.","questions":[{"id":"javascript/dates-temporal-intl/date-pitfalls","number":"010","title":"Why is Date hard to use correctly?","titleHtml":"Why is Date hard to use correctly?","status":"draft","difficulty":"easy","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/dates-temporal-intl/temporal-types","number":"020","title":"What is Temporal, and which type do you use when?","titleHtml":"What is Temporal, and which type do you use when?","status":"draft","difficulty":"medium","frequency":2,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/dates-temporal-intl/intl-formatting","number":"030","title":"How do you format dates, numbers, and plurals per locale with Intl?","titleHtml":"How do you format dates, numbers, and plurals per locale with Intl?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/dates-temporal-intl/time-zones","number":"040","title":"How do you handle time zones correctly?","titleHtml":"How do you handle time zones correctly?","status":"draft","difficulty":"medium","frequency":3,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"24","slug":"json-and-binary-data","title":"JSON and binary data","summaryHtml":"JSON serialization edge cases, and raw memory: ArrayBuffer, typed arrays, and shared memory.","summaryText":"JSON serialization edge cases, and raw memory: ArrayBuffer, typed arrays, and shared memory.","questions":[{"id":"javascript/json-and-binary-data/json-stringify-edge-cases","number":"010","title":"What does JSON.stringify drop or change?","titleHtml":"What does JSON.stringify drop or change?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/json-and-binary-data/json-parse-reviver","number":"020","title":"How do JSON.parse revivers work, and what does source text access add?","titleHtml":"How do JSON.parse revivers work, and what does source text access add?","status":"draft","difficulty":"medium","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/json-and-binary-data/arraybuffer-typed-arrays","number":"030","title":"What are ArrayBuffer, typed arrays, and DataView?","titleHtml":"What are ArrayBuffer, typed arrays, and DataView?","status":"draft","difficulty":"medium","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/json-and-binary-data/modern-binary-data","number":"040","title":"What's new in binary data?","titleHtml":"What's new in binary data?","status":"draft","difficulty":"medium","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/json-and-binary-data/sharedarraybuffer-atomics","number":"050","title":"What are SharedArrayBuffer and Atomics for?","titleHtml":"What are SharedArrayBuffer and Atomics for?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"25","slug":"memory-and-gc","title":"Memory and garbage collection","summaryHtml":"Reachability-based garbage collection, how leaks happen and how to find them, and how V8's collector works.","summaryText":"Reachability-based garbage collection, how leaks happen and how to find them, and how V8's collector works.","questions":[{"id":"javascript/memory-and-gc/garbage-collection","number":"010","title":"How does garbage collection work in JavaScript?","titleHtml":"How does garbage collection work in JavaScript?","status":"draft","difficulty":"medium","frequency":4,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/memory-and-gc/memory-leaks","number":"020","title":"What causes memory leaks, and how do you find them?","titleHtml":"What causes memory leaks, and how do you find them?","status":"draft","difficulty":"medium","frequency":4,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/memory-and-gc/weakref-finalizationregistry","number":"030","title":"What are WeakRef and FinalizationRegistry, and why use them rarely?","titleHtml":"What are WeakRef and FinalizationRegistry, and why use them rarely?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/memory-and-gc/v8-generational-gc","number":"040","title":"How does V8's generational GC work?","titleHtml":"How does V8's generational GC work?","status":"draft","difficulty":"hard","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]},{"number":"26","slug":"inside-the-engine","title":"Inside the engine","summaryHtml":"How V8 turns source into fast machine code — tiers, hidden classes, inline caches — and what makes it slow down.","summaryText":"How V8 turns source into fast machine code — tiers, hidden classes, inline caches — and what makes it slow down.","questions":[{"id":"javascript/inside-the-engine/v8-pipeline","number":"010","title":"What happens between source code and execution in V8?","titleHtml":"What happens between source code and execution in V8?","status":"draft","difficulty":"hard","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/inside-the-engine/hidden-classes-inline-caches","number":"020","title":"What are hidden classes and inline caches?","titleHtml":"What are hidden classes and inline caches?","status":"draft","difficulty":"hard","frequency":3,"core":true,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/inside-the-engine/deoptimization","number":"030","title":"What causes deoptimization?","titleHtml":"What causes deoptimization?","status":"draft","difficulty":"hard","frequency":2,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/inside-the-engine/elements-kinds","number":"040","title":"How does V8 store arrays?","titleHtml":"How does V8 store arrays?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null},{"id":"javascript/inside-the-engine/smi-and-heap-numbers","number":"050","title":"How does V8 represent numbers?","titleHtml":"How does V8 represent numbers?","status":"draft","difficulty":"hard","frequency":1,"core":false,"hasPage":false,"verified":null,"stale":false,"legacy":null}]}]}},"actionData":null,"errors":null}