using & await using (TS 5.2 Explicit Resource Management)

TL;DR

Explanation

using x = getResource() calls x[Symbol.dispose]() when the variable goes out of scope (block end, return, throw). await using x = getResource() calls x[Symbol.asyncDispose]() and awaits it. This enables deterministic cleanup without try/finally boilerplate. Implementing: add [Symbol.dispose]() to your class. Use cases: database connections, file handles, event listeners, locks, timers. The DisposableStack and AsyncDisposableStack helpers manage multiple disposables. Part of the TC39 Explicit Resource Management proposal.

Common Misconception

Why It Matters

Common Mistakes

• Not implementing Symbol.dispose on custom resources.
• Forgetting await using for async cleanup (DB connections, streams).
• Using in non-block scope — using only works in block-scoped contexts.

Code Examples

// Verbose try/finally:
const conn = await db.connect();
try {
    await conn.query('SELECT 1');
} finally {
    await conn.close(); // Easy to forget
}

// TypeScript 5.2+:
class DbConnection implements AsyncDisposable {
    async [Symbol.asyncDispose]() {
        await this.close();
    }
}

async function query() {
    await using conn = await db.connect();
    await conn.query('SELECT 1');
} // conn.close() called automatically

References

• ↗ https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-2.html

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