How to Create a Function in JavaScript

Functions are reusable blocks of code in JavaScript. Here are the different ways to create them.

Method 1: Function Declaration

The traditional way to define a function:

function greet(name) {
  return "Hello, " + name + "!";
}

console.log(greet("Alice")); // "Hello, Alice!"

Method 2: Function Expression

Assign a function to a variable:

const greet = function(name) {
  return "Hello, " + name + "!";
};

console.log(greet("Bob")); // "Hello, Bob!"

Method 3: Arrow Functions (ES6+)

A shorter syntax for writing functions:

const greet = (name) => {
  return "Hello, " + name + "!";
};

// Even shorter for single expressions
const greetShort = (name) => "Hello, " + name + "!";

console.log(greetShort("Charlie")); // "Hello, Charlie!"

Functions with Multiple Parameters

function add(a, b) {
  return a + b;
}

// Arrow function version
const multiply = (a, b) => a * b;

console.log(add(2, 3));      // 5
console.log(multiply(4, 5)); // 20

Default Parameters

function greet(name = "World") {
  return "Hello, " + name + "!";
}

console.log(greet());        // "Hello, World!"
console.log(greet("Alice")); // "Hello, Alice!"

Summary

• Use function declarations for hoisted, named functions
• Use function expressions when assigning to variables
• Use arrow functions for concise syntax and callbacks