Function Callbacks in JavaScript

Introduction to function callbacks

One of the most powerful features of JavaScript, and in fact, the technology that NodeJS was built on, is the concept of callback functions. A callback function is a function that is passed in as an argument to another function and is then generally invoked within the original function. In other words, we are calling a function and telling it to go and do what it needs to do, and when it is finished, to call the function that we have supplied.

Passing a function as an argument

Just as we can pass a value into a function, we can also pass a function into a function as one of its arguments.

This is best illustrated by taking a look at some JavaScript code as follows: