What is a Callback in JavaScript?

What is a Callback in JavaScript?

Ferenc Almasi β€’ πŸ”„ 2020 November 01 β€’ πŸ“– 1 min read

Simply put, callbacks are functions passed as an argument to other functions to be used once an event has occurred or a task is finished. You can think of an on click event listener attached to a DOM element or a callback provided for a network request:

// This function will only run when the event occurs
const onClick = () => console.log('☝️');

document.addEventListener('click', onClick);
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Why do we need callbacks? While JavaScript runs sequentially, (from top to bottom) callbacks lets you execute code in an asynchronousΒ manner. Note that you can also define an anonymous function as a callback, you don't necessarily need to declare it.

// Anonymous function passed as a callback
document.addEventListener('click', () => {
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What are callbacks in JavaScript?
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