Callback Function in JavaScript

A callback function is a function that is passed as an argument to another function and is called later when needed.

Here is a simple example:

function greet(name) {
  console.log("Hello " + name);
}

function processUser(callback) {
  callback("John");
}

processUser(greet);

Output:

Hello John

Here, greet is the callback function because we pass it to processUser().

The processUser() function then calls it using callback("John").

In simple words:

A callback is a function passed to another function to be executed later.