JavaScript | Callbacks
JavaScript c allbacks can be used to process the result of async operation. Lets take a example below. As shown in below example the callback function is used to process the response received from rest service. See the Pen by Rohan ( @rohanlopes20 ) on CodePen . Things gets complicated when we have to call more than one request on after another like second request is depending upon response of first request. This leads to callback hell. I recommend to read more on https://javascript.info/callbacks As you chain more and more calls it becomes complicated to maintained code. This can be avoided with JavaScript Promises. See the Pen by Rohan ( @rohanlopes20 ) on CodePen .