JavaScript Functions Explained

In JavaScript, functions are blocks of code designed to perform a specific task. You can reuse functions, pass arguments, and return values.

1. Function Declaration (Named Function)

This is the most common way to define a function.

Example:

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

console.log(greet("Alice"));

Output

2. Function Expression

Functions can also be assigned to variables.

Example:

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

console.log(greet("Bob"));

Output

3. Arrow Function (ES6+)

A shorter syntax introduced in ES6.

Example:

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

console.log(greet("Charlie"));

Output

One-liner version:

const greet = name => "Hey, " + name;

4. Function with Default Parameters

You can give parameters a default value.

Example:

function greet(name = "Guest") {
  return "Welcome, " + name;
}

console.log(greet()); // No argument passed

Output

5. Function Returning a Value

Functions can return data to be used elsewhere.

Example:

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

let sum = add(5, 7);
console.log(sum);

Output

Summary Table – JavaScript Functions