Optional Chaining and Nullish Defaults

What it is and why to use it

Optional chaining stops a property access or call when its left-hand value is null or undefined. Nullish coalescing supplies a fallback only for those two values. Together they are useful for optional nested data while preserving legitimate values such as zero or an empty string.

Common mistakes and limitations

Optional chaining protects only the nullish part of the chain where it is used. It does not validate unknown data or catch exceptions thrown by a getter or function. Do not use it to hide a field that your program actually requires.

Run this example

Use TypeScript 5.8 or later with strict checking and an ES2022 target. Save each complete example independently as example.ts, compile it, then run the generated JavaScript with a compatible Node.js installation. Compiler-only options below affect checking; they do not add runtime validation.

Terminal — compile and run

npx tsc example.ts --strict --target ES2022 --module commonjs
node example.js

• optional properties
• basic types

Syntax

const city = user.address?.city ?? "Unknown";

Examples

type Settings = { audio?: { volume: number } };
function volume(settings: Settings): number {
  return settings.audio?.volume ?? 50;
}
console.log(volume({}));
console.log(volume({ audio: { volume: 0 } }));

Best practices

• Optional chaining protects only the nullish part of the chain where it is used. It does not validate unknown data or catch exceptions thrown by a getter or function. Do not use it to hide a field that your program actually requires.
• Keep external-input validation separate from compile-time type descriptions.

Runtime & versions

Compiled to JavaScript. Feature availability depends on the language and runtime version used by your project; consult the official reference below.

Related TypeScript documentation

Specifications & further reading

• Official TypeScript documentation