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

Hello, Alice!


2. Function Expression


Functions can also be assigned to variables.

Example:

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

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

Output

Hi, Bob


3. Arrow Function (ES6+)


A shorter syntax introduced in ES6.

Example:

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

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

Output

Hey, Charlie


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

Welcome, Guest


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

12


Summary Table – JavaScript Functions

Type Syntax Style Can Be Named? Introduced In
Function Declaration function name() Yes ES1
Function Expression const name = function() Optional ES1
Arrow Function const name = () => No name by default ES6