What is a Callback function in JavaScript

In this tutorial, we are going to learn about callback functions in JavaScript.

What is a Callback function?

If we call one function that function will call other function by itself is called callback function.

example:

function add(a,b,callback){
   return callback(a,b)
}

add(1,2,function(a,b){
    return a+b;
})

// output  3

Did you notice we have just called add function and that function will call the callback function?

The function which accepts the other function as an argument is called a higher-order function.

Where callback functions are commonly used in JavaScript?

• In Event handling, we commonly used callback functions in JavaScript.

• Network requests.

Consider we have a button with the click event handler is attached to it. The second argument in the addEventListener method is a callback function.

The callback function only invokes when a click event happens on that button.

<button class="btn" >click</button>

<script>
const btn = document.querySelector('.btn');

btn.addEventListener('click',function(){
   alert('someone hit me');
})

</script>