How do you return a parameter

[xwb]

Have a look at the following

function struct () {
   this.value = 0;
}

// Direct parameter
function setdirect (xx) {
   xx += 10;
}

function setindirect (xx) {
   xx.value += 10;
}

var yy = new struct ();
WScript.echo (yy.value);
setdirect (yy.value);
WScript.echo (yy.value);
setindirect (yy);
WScript.echo (yy.value);

What I get is 0 0 10 i.e. setdirect doesn't work but setindirect does.

It looks like the only way I can modify a parameter in a function is to pass a structure to it. Is this assumption correct or is there a "correct" way of modifying a parameter? Is there a way of getting round the call-by-value mechanism?

 

[BillyRayPreachersSon]

You have to pass an object if you want to pass parameters by reference rather than by value... So something like:

var someFunc(xx) {
   xx.myval += 10;
};

var myobj = { myval: 10 };
alert(myobj.myval);
someFunc(myobj);
alert(myobj.myval);

Hope this helps,
Dan

Coedit Limited - Delivering standards compliant, accessible web solutions

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[tsuji]

To: op
If you want (js) official statements, the general rules are these.

Numbers and Boolean values (true and false) are copied, passed, and compared by value.
Objects, arrays, and functions are copied, passed, and compared by reference.

ref

http://windowssdk.msdn.microsoft.com/en-us/library/d53a7bd4.aspx

Substantially the same is given by D Flanagan "Javascript - The Definitive Guide" (4th ed.) section 11.2.

 

[BillyRayPreachersSon]

Except string objects, which are passed by value.

Dan

Coedit Limited - Delivering standards compliant, accessible web solutions

[tt]Dan's Page [blue]@[/blue] Code Couch

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[/tt]

 

[tsuji]

Last, strings are copied and passed by reference, but are compared by value.

Flanagan named it "immutable". ECMA spec also has special note on the special implementation of string for efficient manipulation.

 

[xwb]

From your answers, I guess there isn't if it is a number or boolean. Thanks for the confirmation.