Overview

Allows a function to accept an indefinite number of arguments as an array

You can then access all the passed arguments as an array

Used when you don’t know how many parameters you want to put in

Syntax

function f(a, b, ...theArgs) {
  // …
}

A function definition can only have one rest parameter
The rest parameter must be the last parameter in the function definition
Cannot have a default value

Example

function sum(...theArgs) {
  let total = 0;
  for (const arg of theArgs) {
    total += arg;
  }
  return total;
}
 
console.log(sum(1, 2, 3));
// Expected output: 6
 
console.log(sum(1, 2, 3, 4));
// Expected output: 10

Used to capture all arguments
It’s an array!
- You can use all array methods
primary use case is for creating generic factory functions that accept any function as input and return a new version of the function with some specific modification
- higher-order function: a function that accepts a function and/or returns a function
  - very common in js

Example: logged function factory

function log(inputFunction) {
	return function(...args){
		console.log("Input", args);
		const result = inputFunction(...args);
		console.log("Output", result);
		return result;
	}
}
 
const f = log((a,b) => a + b);
f(1,2);