How to change the value of variable in a function in javascript?

Question

var e = 15;

function change_value(e){

    e = 10;
}

change_value(e);

console.log(e);

The Value of e is still 15.

This is not changing of variable globally take e. and function parameter value set perform only. — Parth Trivedi, Jun 26 '15 at 11:18
There is this answer which can be helpful: http://stackoverflow.com/questions/19721313/javascript-local-and-global-variable-confusion — briosheje, Jun 26 '15 at 11:24

score 4 · Accepted Answer · answered Jun 26 '15 at 11:17

4

The e inside the function scope is different from the e inside the global scope.

Just remove the function parameter:

var e = 15;

function change_value(){
    e = 10;
}

change_value();
console.log(e);

answered Jun 26 '15 at 11:17

Sebastian Nette

7,364
2
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But in my case, i need the value of e variable. e variable is inside another function so I'm passing it. – Shehroz Ahmed Jun 26 '15 at 11:19
You can access the value directly. E.g. `e = e * 10` – Sebastian Nette Jun 26 '15 at 11:21
Yeah you solved my problem, I first declared the variable at the top with null value and then assigned the value. Thank you. – Shehroz Ahmed Jun 26 '15 at 11:23

score 2 · Answer 2 · answered Jun 26 '15 at 11:18

2

javascript does not use reference for simple types. It use a copy method instead. So you can't do this.

You have 2 solutions. This way :

var e = 15;

function change_value(e) {
    return 10;
}

e = change_value(e);

Or this one :

var e = 15;

function change_value() {
    e = 10;
}

But note that this solution is not really clean and it will only works for this e variable.

answered Jun 26 '15 at 11:18

Magus

14,796
3
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I would recommend the OP to go for the first choice. It doesn't have side effect which means the other variable with the same name in even outer scope won't be unintentionally changed. – TaoPR Jun 26 '15 at 11:21

moffeltje · Answer 3 · 2015-06-26T11:20:50.803

1

When you have a parameter in a function, the passed value is copied in the scope of the function and gets destroyed when the function is finished.

all variables in Javascript are created globally so you can just use and modify it without passing it:

var e = 15;

function change_value(){

    e = 10;
}

change_value();

console.log(e);

edited Jun 26 '15 at 11:20

answered Jun 26 '15 at 11:17

moffeltje

4,521
4
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So how can i pass by reference in JavaScript ? we use '&' sign in C++ but how can I do this in JavaScript ? – Shehroz Ahmed Jun 26 '15 at 11:19
@ShehrozSheikh There is no such this as pass by reference in Javascript. – moffeltje Jun 26 '15 at 11:24

score -1 · Answer 4 · answered Jun 26 '15 at 11:23

You can do something like this if you want to assign the passed value to the outer e variable. this is just a sample. In the block you might have any logic in future.

var e = 15;
function change_value(e){

    return e;
}

e = change_value(10);

console.log(e);

But if you want to only call the function and change the e value then remove the parameter from the function because it has different scope then the outer one.

 var e = 15;
 function change_value(){

   e = 10;
}

change_value(10);

console.log(e);

How to change the value of variable in a function in javascript?

4 Answers4