JavaScript Interview Question | Closure

In many interview question nowdays there is a popular interview question based on JavaScript closure and that is:

Input:    messageWord(‘2’)(‘3’)(‘4’)

Output: ‘234’

Solution:

function messageWord (x){

  return function(y){

      return function(z){

        return x + y + z;

      };

  };

}

JavaScript Closure

JavaScript Closure: A closure is the combination of a function (inner function) which have access to the parent scope (outside function variable).            

Advantages of closure:

1)      In the object-oriented programming paradigm, encapsulation is one of the key features. Encapsulation hides the inner work of an object from the outside world. But as JavaScript is a scripting language it doesn’t have encapsulation feature.

Here Closure comes in a picture, with the help of “Closure” we can access the parent function variable and arguments.

2)      Example:

var myFun = (function () {

    var privateFun = function () {

        alert(' privateFun ');

    }

    return {

        publicFun : function () {

            privateFun();

        }

    }

})();

In this example, I can access the publicFun but not privateFun.

3)      Closures are helpful in APIs callback functions requirement.

There are many examples available for closure, if you want to explore more.