TIL: `using` — TypeScript Built-in Resource Cleanup

TypeScript 5.2 shipped an implementation of the TC39 Explicit Resource Management proposal (now Stage 4). The key addition is using: a declaration that automatically calls a cleanup method when the enclosing block exits — even on throw.

The Problem

Cleanup code is easy to forget or nest awkwardly:

const conn = await db.connect();
try {
  const rows = await conn.query('SELECT * FROM users');
  // ... work ...
} finally {
  conn.release(); // must remember this every time
}

How using Works

An object is disposable when it has a [Symbol.dispose]() method. Declare it with using and TypeScript emits a try/finally automatically:

class DbConnection implements Disposable {
  [Symbol.dispose]() {
    this.release();
  }
}

function fetchUsers() {
  using conn = new DbConnection();
  return conn.query('SELECT * FROM users');
} // conn[Symbol.dispose]() runs here, even if query throws

For async teardown use await using with Symbol.asyncDispose:

class DbConnection implements AsyncDisposable {
  async [Symbol.asyncDispose]() {
    await this.close();
  }
}

async function fetchUsers() {
  await using conn = await db.connect();
  return conn.query('SELECT * FROM users');
} // conn[Symbol.asyncDispose]() is awaited on exit

Composing Resources with DisposableStack

When you open several resources, DisposableStack registers them and disposes in reverse order:

function processData() {
  using stack = new DisposableStack();
  const file = stack.use(openFile('data.csv'));
  const conn = stack.use(openDbConnection());
  // ... work ...
} // conn disposed first, then file

AsyncDisposableStack works the same way for async disposables.

tsconfig Setup

Add esnext.disposable (or just esnext) to lib:

{
  "compilerOptions": {
    "lib": ["ES2022", "esnext.disposable"],
    "target": "ES2022"
  }
}

TypeScript exposes Disposable, AsyncDisposable, DisposableStack, and AsyncDisposableStack automatically once the lib entry is present.

Runtime Support

| Environment | Native support | |---|---| | TypeScript ≥ 5.2 | Yes (emits try/finally for older targets) | | Node.js ≥ 22 | Yes (V8 12.1+) | | Node.js 20 | Partial — Symbol.dispose exists, stack classes need polyfill | | Chrome / Edge ≥ 125 | Yes | | Firefox | Not yet |

TypeScript handles the down-emit, so you can use using today in any Node.js or browser project — the generated output is a plain try/finally.