Closures in JavaScript

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In this video we will understand closures in JavaScript with an example.

What is a closure
A closure is an inner function that has access to the outer function’s variables in addition to it's own variables and global variables. The inner function has access not only to the outer function’s variables, but also to the outer function’s parameters. You create a closure by adding a function inside another function.

JavaScript Closure Example

function addNumbers(firstNumber, secondNumber)
{
var returnValue = "Result is : ";
// This inner function has access to the outer function's variables & parameters
function add()
{
return returnValue + (firstNumber + secondNumber);
}
return add();
}

var result = addNumbers(10, 20);

Output : Result is : 30

The following code Returns the inner function expression

function addNumbers(firstNumber, secondNumber)
{
var returnValue = "Result is : ";
function add()
{
return returnValue + (firstNumber + secondNumber);
}
// We removed the parentheses. This will return the inner function expression without executing it.
return add;
}

// addFunc will contain add() function (inner function) expression.
var addFunc = addNumbers(10, 20);
// call the addFunc() function and store the return value in result variable
var result = addFunc();

Returning and executing the inner function

function addNumbers(firstNumber, secondNumber)
{
var returnValue = "Result is : ";
function add()
{
return returnValue + (firstNumber + secondNumber);
}
// We removed the parentheses. This will return the inner function add() expression without executing it.
return add;
}

// This returns add() function (inner function) definition and executes it. Notice the additonal parentheses.
var result = addNumbers(10, 20)();

[asifkamranmalick]

This was very well explained. I've seen other people over-complicating the topic while explaining. Short and sweet. Thanks a lot.

[isunas]

You are a vey good teacher.you explain concepts very clear.thank u so much

[someshnukala]

sir! no words. simply super explanation. Great sir. Thank you so much sir.

[gudapruthvihemanth]

Beautifully explained. Great..!! Thanks a lot. Keep

[Knowideer]

super tutorial on closures! many thanks!

[abdulshabbir]

Thank you so much! I finally understand closures!

[Saravana.Kumar.]

Nice way of teaching bro! thanks for doing it, keep doing it.

[shahnawazatharkazmi]

respected venkat sir, we need reporting like crystal report + jquery .plz do as soon.thanx in advanced

[muhammadzarshid]

Sir could we expect Reports in Asp.net.it may be crystal report. Thanks for effort is ur excellency 👍

[priyankashah]

Thank you for such a nice explanation. I have a question, what happens if we remove return add from the addNumbers function without changing any code?

[shashwatgupta]

please make few video on "JavaScript Scoping and Hoisting"
I really need that videos

[hookbanner]

Somehow this didn't work for me. May be this is mozilla firefox issues, so I made a little change.
function y(a, b){
var ResultIs = "Result is ";
return(function xek()
{
return ResultIs + (a+b);
});
}
var x = y(5, 6)();
document.write(x);
And it had started to work.

[hk_build]

can anybody tell me when i need to use closures...? and give me real world example where closure exist..?