What are Callbacks in JavaScript?

Callbacks are a fundamental concept in JavaScript, especially when dealing with asynchronous operations. This article aims to provide a clear understanding of what callbacks are and how to use them in JavaScript.

What are Callbacks?

In JavaScript, functions are first-class objects. This means that functions can be passed as arguments to other functions, returned by other functions, and assigned as values to variables. A callback function is a function that is passed as an argument to another function and is executed after some operation has been completed. Hence, the function "calls back" into the other function. Callbacks are often used when dealing with asynchronous operations.

How Do Callbacks Work?

Here's a simple example of a callback function:

function greeting(name) {
  console.log(`Hello, ${name}`)

function processUserInput(callback) {
  const name = prompt('Please enter your name.')


In the above example, greeting is a callback function. It's passed as an argument to processUserInput and is called within processUserInput with the user's name as an argument.

Why Use Callbacks?

Callbacks are used for asynchronous operations. They allow you to ensure that certain code doesn't execute until other code has already finished execution.

Practical Examples of Callbacks

Here's an example of a callback function used with an asynchronous operation:

function downloadData(url, callback) {
  // simulate an asynchronous operation
  setTimeout(() => {
    const data = `Data from ${url}`
  }, 2000)

function processData(data) {

downloadData('http://example.com', processData)

In this example, processData is a callback function that's passed to downloadData. It's called within downloadData after the simulated download operation has completed.

Understanding callbacks can help you write more efficient and organized JavaScript code, especially when dealing with asynchronous operations.