Lokesh

Posted on Oct 12

Types of Functions in JavaScript

#javascript #frontend

What Is a Function?

A function is a reusable block of code that performs a particular task.

Instead of writing the same code again and again, we can create a function and call it whenever we need it.

JavaScript has different ways to create and use functions. Let's understand some common types with simple examples.

A function declaration is a common way to create a function using the function keyword.

function greet() {
    console.log("Hello World!");
}

greet();

Output:

Hello World!

Here, we create a function named greet and call it to execute the code inside it.

Parameters allow us to pass information into a function.

function greet(name) {
    console.log("Hello " + name);
}

greet("John");

Output:

Hello John

Here, name is a parameter, and "John" is the argument passed to the function.

The return statement sends a result back to the place where the function was called.

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

let result = add(10, 20);
console.log(result);

Output:

This is useful when we want to calculate a value and use it somewhere else in our program.

A function expression is created by assigning a function to a variable.

const greet = function() {
    console.log("Welcome!");
};

greet();

Output:

Welcome!

Unlike a function declaration, this function expression cannot be called before the variable is initialized.

Arrow functions provide a shorter way to write functions.

const add = (a, b) => {
    return a + b;
};

console.log(add(5, 10));

Output:

For simple functions, we can write it even shorter:

const add = (a, b) => a + b;

Arrow functions are commonly used in modern JavaScript, especially with array methods such as map() and filter().

An anonymous function is a function without its own name.

setTimeout(function() {
    console.log("Hello!");
}, 1000);

Here, the anonymous function runs after approximately one second.

Anonymous functions are often used as callbacks, where a function is passed to another function.

Functions help us: