Typed Rest Parameters

What it is and why to use it

A rest parameter gathers any remaining arguments into an array. Its annotation describes that array, not a single argument. It is useful for a small function that accepts a variable number of values while checking every supplied value’s type.

Common mistakes and limitations

A rest parameter must be last. number[] permits any number of numeric arguments, while a rest tuple can constrain the exact positions and count. Avoid unchecked any[] when the function expects known element types.

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

• arrays tuples
• variadic tuples

Syntax

function sum(...values: number[]): number;

Examples

function total(label: string, ...values: number[]): string {
  return label + ": " + values.reduce((sum, value) => sum + value, 0);
}
console.log(total("Scores", 3, 4, 5));
console.log(total("Empty"));

Best practices

• A rest parameter must be last. number[] permits any number of numeric arguments, while a rest tuple can constrain the exact positions and count. Avoid unchecked any[] when the function expects known element types.
• 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