es-toolkit/docs/reference/function/rest.md

rest

Creates a function that transforms the arguments of the provided function func. The transformed arguments are passed to func such that the arguments starting from a specified index are grouped into an array, while the previous arguments are passed as individual elements.

Signature

function rest<F extends (...args: any[]) => any>(func: F, startIndex: number): (...args: any[]) => ReturnType<F>;

Parameters

• func (F): The function whose arguments are to be transformed.
• startIndex (number, optional): The index from which to start grouping the remaining arguments into an array. Defaults to func.length - 1, grouping all arguments after the last parameter.

Returns

((...args: any[]) => ReturnType<F>): A new function that, when called, returns the result of calling func with the transformed arguments.

• The transformed arguments are:
  • The first start arguments as individual elements.
  • The remaining arguments from index start onward grouped into an array.

Examples

function fn(a, b, c) {
  return Array.from(arguments);
}

// Using default start index (func.length - 1, which is 2 in this case)
const func1 = rest(fn);
console.log(func1(1, 2, 3, 4)); // [1, 2, [3, 4]]

// Using start index 1
const func2 = rest(fn, 1);
console.log(func2(1, 2, 3, 4)); // [1, [2, 3, 4]]

// With fewer arguments than the start index
console.log(func1(1)); // [1, undefined, []]