Variadic calculations
A function must accept a variable number of numeric inputs.
JS Puzzles · Const
rest parameters
Rest parameters let a function accept any number of arguments by gathering the remaining arguments into an array. They are written with ... before the final parameter name.
How it works
A rest parameter is written as three dots before the final parameter name in a function declaration. When the function runs, any arguments not assigned to earlier named parameters are collected into that parameter as a real array, so array methods can be used directly.
Syntax
function name(...rest) { /* body */ }Parameters
| Name | Type | Description |
|---|---|---|
args | parameters | Named parameters before the rest parameter receive their corresponding arguments. |
...rest | array | The final rest parameter receives all remaining arguments in an array. |
Returns
The page does not specify a general return value; the function's own return statement determines its result.
Key points
- Arguments are gathered into one array rather than being exposed as separate named parameters.
- Functions can receive more arguments than their explicitly named parameters; a rest parameter captures the extras.
- Use rest parameters when designing variadic functions whose input count is not fixed.
- The meaning of
...depends on its position: at the end of a function parameter list, it is rest syntax.
Common mistakes
- A rest parameter must be the function's final parameter; placing another parameter after it is invalid.
Example: Collecting arguments with a rest parameter
function sum(...numbers) {
return numbers.reduce((total, number) => total + number, 0);
}
console.log(sum(2, 4, 6)); // 12The rest parameter gathers all arguments after the function's named parameters into an array.
When to use it
Argument forwarding
A wrapper forwards an arbitrary number of arguments to another function.
Flexible collection processing
A utility needs direct access to array methods while processing extra inputs.
Related
spread syntaxargumentsfunction parameters