Configuring target and lib

target selects the JavaScript language level TypeScript emits; lib selects standard API declarations available to the checker. They are related but not identical: including dom allows browser types, but does not create DOM APIs in Node.js. Select a runtime-compatible target and libraries without assuming a polyfill is installed.

The example uses modern Array APIs declared by an appropriate ES library. A modern runtime implements them, but an older runtime could require a polyfill even when TypeScript checks the calls successfully.

Adding "DOM" to lib will not make document exist in a Node process; libraries change declarations, not the environment.

Save as configuring-target-lib.ts. The following program passed strict TypeScript compilation, and the displayed output was captured by executing its emitted JavaScript with Node.js 22.16.0.

TypeScript source

const names: string[] = ["Ada", "Lin", "Maya"];
console.log(names.at(-1));
console.log(names.includes("Lin"));

Verified output

Maya
true

Compile: npx tsc --strict --target es2022 --module commonjs configuring-target-lib.ts; run: node configuring-target-lib.js. For Node.js API examples, install @types/node first. For browser projects, use the browser-specific instructions below.

The example demonstrates the code-level behavior; the related configuration or test commands are shown separately when needed.

The example uses modern Array APIs declared by an appropriate ES library. A modern runtime implements them, but an older runtime could require a polyfill even when TypeScript checks the calls successfully.

Predict what changes if you alter one input. Then run the code to compare your reasoning with the real output.

Practical project lab: These are real configuration and source-file examples, not a TypeScript object that merely describes settings. Place the files at the named paths relative to one project directory.

tsconfig.json

{"compilerOptions":{"target":"ES2022","lib":["ES2022","DOM"],"module":"ES2022","strict":true}}

main.ts

const element = document.querySelector("h1");
console.log(element?.textContent);

Commands

npx tsc --noEmit -p .

DOM declarations enable compiling the browser code; run the emitted code in a browser, not Node.

This local compiler or test-runner mini-project was validated in addition to the primary program.

Adding "DOM" to lib will not make document exist in a Node process; libraries change declarations, not the environment.

Identify whether the failure is a type-checking issue, a configuration issue, or a runtime behavior issue before choosing a fix.

Type-check the sample with lib es2022,dom; compare diagnostics after selecting an older ES-only lib.

Write down your expected result first. For configuration examples, compare compiler output and diagnostics; for test examples, make the assertion fail deliberately to verify that the tool reports it.

For the exact current options and platform behavior, consult the official documentation. These examples were verified using the tool versions described above.

target selects the JavaScript language level TypeScript emits; lib selects standard API declarations available to the checker.

Run the primary example, then complete the practice task or environment-specific lab.