JavaScript Callbacks

In JavaScript since functions are objects so we can pass them as parameter to another functions. These functions can then be called inside another functions and the passed function is referred as callback function.

Following is the code for JavaScript Callbacks −

Example

<!DOCTYPE html>
<html>
<head>
<style>
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   }
</style>
</head>
<body>
<h1>JavaScript Boolean constructor Property</h1>
<p class="sample"></p>
<button class="btn">CLICK HERE</button>
<h3>
Click on the above button to call the add function which calls back
another function
</h3>
<script>
   function add(a, b, callback) {
      callback(a + b);
   }
   function multiplyResultByTwo(res) {
      document.querySelector(".sample").innerHTML = res * 2;
   }
   document.querySelector(".btn").addEventListener("click", () => {
      add(4, 5, multiplyResultByTwo);
   });
</script>
</body>
</html>

Output

JavaScript Callbacks

On clicking the “CLICK HERE” button −

JavaScript Callbacks