I want to be able to modify the arguments passed to a self executing function.

Here is some sample code:

var test = 'start';
(function (t) {t = 'end'} )(test);
alert(test) //alerts 'test'

And here is a fiddle. The variable test has not changed. How can I alter it, as in pass-by-reference?

I want to be able to modify the arguments passed to a self executing function.

Here is some sample code:

var test = 'start';
(function (t) {t = 'end'} )(test);
alert(test) //alerts 'test'

And here is a fiddle. The variable test has not changed. How can I alter it, as in pass-by-reference?

• javascript
• pass-by-reference
• anonymous-function
• self-executing-function

Share Improve this question Follow asked Apr 4, 2013 at 22:18 tckmntckmn 59.4k2727 gold badges118118 silver badges156156 bronze badges

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4 Answers 4

Sorted by: Reset to default 10

Pass in an object, it is pass-by-reference:

var test = {
    message: 'start'
};
(function (t) {t.message = 'end'} )(test);
alert(test.message)

FYI, Array is also pass-by-reference.

You cannot do that (well, precisely that) in JavaScript. You can do something like this, however:

 var testBox = { test: "hello" };
 (function(tb) { tb.test = "goodbye"; })(testBox);
 alert(testBox.test); // "goodbye"

JavaScript only has pass-by-value in function calls; there's only one corner-case way to have an alias to something like a variable (the arguments object and parameters), and it's sufficiently weird to be uninteresting.

That said, object properties are (usually) mutable, so you can pass object references around in cases where you need functions to modify values.

You can't do this.

The best you can do is pass in an object, and then update that object.

var test = { state: 'start' };
(function (t) {t.state = 'end'} )(test);
alert(test.state); // 'end'

you are just passing the value of test variable as an argument to the function. After changing the argument's value you need to assign back to the test variable.

var test = 'start';
(function (t){t = 'end'; test = t;} )(test);
alert(test) //alerts 'test'

Or

var myObject = {test: "start"};
var myFunc = function (theObject){
    theObject.test = 'end';
}(myObject);
alert(myObject.test);