JavaScript Callback Functions

By onjsdev

Dec 5th, 2023

In Javascript, callbacks play a crucial role in handling asynchronous operations. In this guide, we'll explore what callback functions are, how they work, and how you can use them in JavaScript.

What are Callback Functions?

A callback function is a function that is passed as an argument to another function. It is executed after the completion of a specific task.

In simpler terms, it's a way to ensure that a certain piece of code is only executed once another operation has finished.

Basic Syntax

function doSomething(callback) {
  // Code to perform some task
  // Callback function is executed

// Using the function with a callback
doSomething(function() {
  console.log('Task is complete!');

In this example, doSomething is a function that takes a callback function as an argument. Once doSomething completes its task, it executes the provided callback function.

How To Handle Asynchronous Operations With Callbacks

Callbacks are often used to handle asynchronous operations, such as fetching data from a server or reading a file.

Here's a simple example using setTimeout:

function delayedGreeting(callback) {
  setTimeout(function() {
    console.log('Hello, world!');
  }, 1000);

// Using the function with a callback
delayedGreeting(function() {
  console.log('Callback executed after the greeting!');

In this example, the delayedGreeting function simulates a delay and then executes the provided callback once the delay is over.

Callback Functions As A Variable

In JavaScript, functions are considered first-class citizens, meaning they can be passed around like any other value. This feature allows callbacks to be assigned to variables and passed as arguments easily:

const myCallback = function() {
  console.log('This is my callback!');

function executeCallback(callback) {

// Using the function with a callback variable

Arrow Callback Functions

With the introduction of arrow functions in ES6, writing callbacks became even simpler:

// Using an arrow function as a callback
doSomething(() => {
  console.log('Task is complete!');


You now have a basic understanding of JavaScript callback functions. As you dive into web development, you'll encounter more complex scenarios where callbacks play a crucial role in managing asynchronous operations. Keep exploring and practicing.

Thank you for reading.