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?

When we call a 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, in the above code we have called the 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>