...rest: T[] Rest Parameters
Last updated: 2026-10-22
...rest: T[] Rest Parameters
Rest parameters (...scores: number[]) collect all remaining arguments into a real array, letting a function accept any number of same-typed arguments — the type-safe replacement for arguments.
| Group | Functions & Classes |
|---|---|
| Kind | Syntax |
| Strict mode | Not required |
ℹ️ Info The editor transpiles TypeScript to JavaScript and runs it (no type checking); see each example's Output for type-check results.
📝 Syntax
function average(...scores: number[]): number {
if (scores.length === 0) return 0;
return scores.reduce((sum, s) => sum + s, 0) / scores.length;
}
// Positional + rest: the rest parameter must be last
function logRequest(method: string, ...fields: string[]): void;⚙️ Parameters
| ...scores: number[] | Rest parameter: all remaining arguments are collected into a number[]; must be the last item in the list |
|---|
Returns：Same as ordinary functions: annotate explicitly or infer from the body; a rest parameter changes nothing about return typing.
▶ Example
Edit the code below and click Try it to see the transpiled result:
Output：
84.3
97.5
0
(Runtime output after transpilation; average("90") is a compile error — rest elements must be number)💡 Notes
ℹ️ Info Rest parameters are real arrays at runtime — map/filter/reduce work directly. Far safer than the legacy arguments object (array-like and untyped).
⚠️ Note ...args: any[] throws away all element types; prefer concrete element types, or a generic tuple ...args: T to keep positions typed.
💡 Tip Tuple types can pin down rest parameters: ...args: [name: string, retries: number] means argument 1 must be string and argument 2 number.
🏷️ Related Functions & Classes
💡 Related cases
More cases coming soon.
📚 Related tutorials
❓ FAQ
Q ...scores: number[] vs scores: number[] — what's the difference?
A The latter is one array parameter: average([90, 85]). The former accepts any number of number arguments: average(90, 85). If callers already hold an array, a plain array parameter fits better.
Q Can a rest parameter go in the middle?
A No. It must be last — "rest" by definition collects everything after it; the compiler rejects it anywhere else.
Q What are generic rest parameters for?
A <T extends any[]>(...args: T) collects arguments as a tuple, preserving each position's type — the key trick for wrap/decorate utilities that forward arguments.
