What is the difference between target, lib, and module?

Three independent settings, each answering a different question.

• target: which JavaScript syntax may appear in the output. Newer syntax is rewritten (??, **, optional chaining, class fields) and anything the target already supports is left alone. It also sets the default lib and the default for useDefineForClassFields (on from ES2022).
• lib: which built-in declarations the type checker knows about: Array.prototype.at, Object.hasOwn, Promise, and the dom types. It produces no output at all. Setting lib replaces the default list, so "lib": ["es2022"] also drops dom.
• module: which module format the emitted import/export takes (commonjs, esnext, preserve, nodenext). It also steers module resolution defaults. It has no say over syntax such as ??.

tsc never polyfills. Syntax is transformed; APIs are not. [1].at(0) is emitted unchanged even for target: es2015. If lib says an API exists but the runtime lacks it, you get a runtime TypeError, not a compile error. So set lib to what your real runtime provides (or what your polyfills add), and target to the oldest syntax that runtime can parse.

Defaults, by version: in 5.9 target defaulted to ES5 and module to CommonJS. TS 6.0 changed these to a floating latest target (es2025 on 6.0 and 7.0) and module: esnext. target: es5 is deprecated in 6.0 and an error in 7.0.

Practical picks: Node runs the output, so module: nodenext and a target matching the Node version. A bundler consumes it, so module: preserve, noEmit, and a target as modern as the bundler's input. Community baselines live in tsconfig/bases.

// a.ts, TypeScript 7.0.2 (b.ts exports `helper`)
import { helper } from "./b";
export const last = [1, 2, 3].at(-1) ?? helper;
export const cube = last ** 3;
export const has = Object.hasOwn({ a: 1 }, "a");

// tsc --target es2015 --lib es2015 --module esnext
// Error TS2550: Property 'at' does not exist on type 'number[]'. Do you need to change your target library? Try changing the 'lib' compiler option to 'es2022' or later.
// Error TS2550: Property 'hasOwn' does not exist on type 'ObjectConstructor'. ...
// → export const last = (_a = [1, 2, 3].at(-1)) !== null && _a !== void 0 ? _a : helper;
// → export const cube = Math.pow(last, 3);
// → export const has = Object.hasOwn({ a: 1 }, "a");

// tsc --target es2022 --module commonjs --moduleResolution bundler
// → const b_1 = require("./b");
// → exports.last = [1, 2, 3].at(-1) ?? b_1.helper;
// → exports.cube = exports.last ** 3;

The first compile also wrote the JavaScript above (errors do not stop emit unless noEmitOnError is set). ?? and ** were rewritten for ES2015, while .at and Object.hasOwn were left as written, whatever lib said.

• Treating target as a polyfill switch. Lowering it never adds missing APIs; only syntax changes.
• Setting lib: ["es2022"] and then using document or window. dom is no longer included (TS2584, checked on 7.0.2 and 5.9.3).
• Assuming module and target move together. On 7.0.2 and 6.0.3, --module nodenext still compiled using declarations down; on 5.9.3 it left them as written. The TSConfig reference still says nodenext "implies the floating --target esnext", so ❓ the page is out of date for 6.0+.
• Upgrading from 5.x with no target or module in the config. The same file compiled to CommonJS on 5.9.3 and to ES module output on 6.0.3 and 7.0.2.