What is Callback in JavaScript

A callback is a plain JavaScript function passed to some other function as an argument or option. In JavaScript, functions are objects. Because of this, a function can take another function as a parameter and calls it inside. This is why we call it a “callback“. Let’s understand this with an example:

var message = function() {  
    console.log("This message will be shown after 1 second");
}
setTimeout(message, 1000); // message is callback function here

A callbacks could be anonymous function too. We can define a function directly inside another function, instead of calling it. Checkout the following example:

setTimeout(function() {  
    console.log("This message will be shown after 1 second");
}, 1000);

The output of the above two examples will be same.

Callback Using ES6 Arrow Function:

setTimeout(() => { 
    console.log("This message will be shown after 1 second");
}, 1000);

Note: The setTimeout is JavaScript’s inbuilt function which calls a function or evaluates an expression after a given period of time (in milliseconds).

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