For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/function/rest.md.
Install massaman

    rest es-toolkit

    Creates a new function that bundles parameters from a specific index into an array and passes them to the function.

    const restFunc = rest(func, startIndex);

    Usage

    rest(func, startIndex?)

    Use rest when you want to bundle the remaining parameters into an array. Parameters before the specific index are passed individually, and parameters after are bundled into an array.

    This is useful for creating functions that accept variable parameters or when you want to change how existing functions handle parameters.

    import { rest } from 'es-toolkit/function';

// Basic usage (bundle from the last parameter into an array)
function sum(a: number, b: number, numbers: number[]) {
  return a + b + numbers.reduce((sum, n) => sum + n, 0);
}

const restSum = rest(sum); // startIndex defaults to func.length - 1 (2)
console.log(restSum(1, 2, 3, 4, 5)); // 1 + 2 + (3 + 4 + 5) = 15
// The sum function is called with [1, 2, [3, 4, 5]]

// Bundle into an array starting from a different index
function logMessage(level: string, messages: string[]) {
  console.log(`[${level}] ${messages.join(' ')}`);
}

const restLog = rest(logMessage, 1); // Bundle from index 1
restLog('INFO', 'Application', 'started', 'successfully');
// Called as logMessage('INFO', ['Application', 'started', 'successfully'])

// Practical example: first parameter individual, rest as an array
function format(template: string, values: any[]) {
  return values.reduce((result, value, index) => {
    return result.replace(`{${index}}`, value);
  }, template);
}

const restFormat = rest(format, 1);
console.log(restFormat('Hello {0}, welcome to {1}!', 'John', 'our site'));
// 'Hello John, welcome to our site!'

    It also handles cases where there are fewer parameters.

    import { rest } from 'es-toolkit/function';

function greet(greeting: string, name: string, extras: string[]) {
  const extraText = extras.length > 0 ? ` ${extras.join(' ')}` : '';
  return `${greeting} ${name}!${extraText}`;
}

const restGreet = rest(greet);

console.log(restGreet('Hello', 'Alice', 'Have a great day!'));
// 'Hello Alice! Have a great day!'

console.log(restGreet('Hi', 'Bob'));
// 'Hi Bob!' (extras becomes an empty array)

console.log(restGreet('Hey'));
// 'Hey undefined!' (name is undefined, extras is an empty array)

    Parameters

    funcFrequired

    The function to change parameter handling.

    startIndexnumberoptional

    The index from which to start bundling into an array. Defaults to func.length - 1, bundling from the last parameter.

    Returns

    Returns a new function that bundles parameters from a specific index into an array and passes them to the original function.

    (...args: any[]) => ReturnType<F>
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.