Checking JavaScript in Node.js, Deno and Bun

The same file in three runtimes

The file below uses only web APIs (Request, Response, URL), which all three runtimes provide, so the same code runs on each. Its types are JSDoc, so it runs as written everywhere; the question is only which checker reads the comments. This site checks it with tsc 5.9, and the second version shows the mistake every checker reports:

/** @typedef {{ path: string, method: string }} Echo */

/**
 * Answers every request with its path and method, as JSON.
 * @param {Request} request
 * @returns {Response}
 */
export function handle(request) {
  const url = new URL(request.url);
  /** @type {Echo} */
  const body = { path: url.pathname, method: request.method };
  return Response.json(body);
}

/** @typedef {{ path: string, method: string }} Echo */

/**
 * Answers every request with its path and method, as JSON.
 * @param {Request} request
 * @returns {Response}
 */
export function handle(request) {
  const url = new URL(request.url);
  /** @type {Echo} */
  const body = { path: url.pathnme, method: request.method };error TS2551: Property 'pathnme' does not exist on type 'URL'. Did you mean 'pathname'?
  return Response.json(body);
}

None of the three runtimes reports that typo when it runs the file: per their documentation, Node.js does not check types at all, and Deno and Bun check only when asked. The program starts, and fails on the first request.

Node.js

Node.js runs JavaScript and, since 22.18 and 23.6, .ts files with their types erased (JSDoc vs Node’s type stripping). It checks neither. The check is tsc, installed as a development dependency and run with your config:

npm install --save-dev typescript @types/node
npx tsc -p jsconfig.json

The Node.js setup has the config, including types: ["node"] for @types/node.

Deno

Deno ships TypeScript’s checker. Per its documentation, deno run stopped checking by default in 1.23 (deno run --check turns it back on), and deno check checks without running. JavaScript files are checked only when you ask: checkJs in the config, // @ts-check in the file, or deno check --check-js:

deno check --check-js main.js

Since 2.1, Deno reads a jsconfig.json or tsconfig.json when the project has a package.json, so the same config can serve tsc and Deno; a deno.json with compilerOptions takes precedence when both exist. The Deno setup covers both. Deno’s own APIs (Deno.serve) are typed by deno check only: tsc does not know them.

Bun

Per Bun’s documentation, Bun runs JavaScript and TypeScript without checking types. Since Bun 1.4.3 (10 October 2026), bun check checks a project from its tsconfig.json and writes nothing, and bun run --check checks before running; the release post describes the checker as a port of TypeScript 7’s. It reports errors in JavaScript files when checkJs is on, and its documentation does not mention jsconfig.json:

bun check

tsc works on Bun projects too, with @types/bun for Bun’s APIs; the Bun setup checks its example that way. We have not run bun check.

One checker or three

Every runtime here leaves type errors to a separate step, so the practical question is which checker your CI runs. Running tsc everywhere gives one TypeScript version, pinned in package.json, for the editor, CI and every developer. The runtimes’ own checkers save an install, at the cost of following their own release schedule for TypeScript: Deno’s built-in version, and Bun’s port of TypeScript 7, can differ from the typescript your editor runs.