Object copying 1

[jtaal]

Hi all,

Is there a way to make the following script work as i would expect it to?

<script language="javascript">
function constr () {
  this.value = 'oldval';
  this.someotherval = 'xxx';
}

var obj = new constr ();
obj.someotherval ='yyy';
var obj2 = obj;
obj2.value = 'newval';
alert(obj.value);
</script>

I would expect an alert ('oldval'); but instead newval is alerted.
I think javascript uses (alot) of Cpointer-like (or C++reference-like) copying.
Is there a way to let javascript do some real copying???

 

[jemminger]

according to my js book, objects are reference values and so copying is done by reference. the solution is to make your own copy method:

<script language="javascript">

function constr () {
  this.value = 'oldval';
  this.someotherval = 'xxx';
}

function realCopy(o) {
	var tmp = new Object();
	
	for (p in o)
		tmp[p] = o[p];
	
	return tmp;
}


var obj = new constr ();
obj.someotherval ='yyy';

var obj2 = realCopy(obj);
obj2.value = 'newval';

alert(obj.value);

</script>

=========================================================
-jeff

http://www.jeffemminger.com

try { succeed(); } catch(E) { tryAgain(); }

 

[jtaal]

I already thought of this. The only problem is that I hav recursive objects and i want them to be copyed (not reffed) as well. I don't think this will work for my application.

 

[jtaal]

<script language="javascript">

function constr () {
  this.value = Object ();
  this.value.val = 'oldval';
  this.someotherval = 'xxx';
}

function realCopy(o) {
    var tmp = new Object();
    
    for (p in o)
        tmp[p] = o[p];
    
    return tmp;
}


var obj = new constr ();
obj.someotherval ='yyy';

var obj2 = realCopy(obj);
obj2.value.val = 'newval';

alert(obj.value.val);
</script>

 

[theboyhope]

I can't really add much to that but I was gonna suggest a slightly different function.

function objCopy( sourceObj ) {

	for( var prop in sourceObj ) {
		this[ prop ] = sourceObj[ prop ];
	}
}

var obj = new constr ();
var obj2 = new objCopy( obj );

Same difference, eh.

 

[jtaal]

Could i try something with a recursive (?) function that copies with a special copy if the type is an Object and normal copy else?
Does an Array has the same behaviour???

 

[theboyhope]

Just had the same thought. Off to try it.

 

[theboyhope]

Seems to work okay.

function objCopy( sourceObj ) {

	for( var prop in sourceObj ) {

		if ( typeof sourceObj[ prop ] == "object" )
			this[ prop ] = new objCopy( sourceObj[ prop ] );
		else
			this[ prop ] = sourceObj[ prop ];
	}
}

HTH.

 

[jtaal]

This is awesome, working around javascripts reference copying. Do you know if the same behaviour goes for the Array () object?

 

[theboyhope]

That example should already work with an array.