What is callback hell and how can it be avoided?

When a JavaScript developer tries to execute multiple asynchronous operations then sometimes issues arise and it is termed callback hell. 

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How to escape from a callback hell?

JavaScript gives an easy way of avoiding callback hell. This is performed by event queue and promises.

• Promises
• Async/Await

Example of Callback Hell

getDataFromFunction1(function(x){
    getDataFromFunction2(x, function(y){
        getDataFromFunction3(y, function(z){
            ...
        });
    });
});