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What is callback hell in Node.js ?

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Node.js Callback hell is a phenomenon that afflicts a JavaScript developer when he tries to execute multiple asynchronous operations one after the other.

An asynchronous function is one where some external activity must complete before a result can be processed; it is “asynchronous” in the sense that there is an unpredictable amount of time before a result becomes available. Such functions require a callback function to handle errors and process the result.

See the following example:-

getData(function(a){

    getMoreData(a, function(b){

        getMoreData(b, function(c){ 

            getMoreData(c, function(d){ 

            getMoreData(d, function(e){ 

            ...

        });

        });

        });

    });

});

There are following techniques to avoid callback hell:-

  1. Using Async.js
  2. Using Promises
  3. Using Async-Await

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