Functions

Function declaration

javascript
function add(a, b) {
  return a + b;
}
add(2, 3);  // 5

Function expression

javascript
const multiply = function (a, b) {
  return a * b;
};

Arrow functions

javascript
const add = (a, b) => a + b;
const double = x => x * 2;

Short body can omit return. For a block body use { } and explicit return.

Parameters and arguments

Default parameters:

javascript
function greet(name = \"Guest\") {
  return `Hello, ${name}`;
}

Rest parameters:

javascript
function sum(...nums) {
  return nums.reduce((a, b) => a + b, 0);
}