Javascript Object 'location' Pointer?

likwid · 2 Sep 2008 at 15:06

Hi

It maybe I'm barking up the wrong tree here but i'll try and explain what I'm trying to do.

I'm trying to update an object, rather an element within an object, and would like to be able to store the location as a variable.

For example:

ref = Object[cat1][cat2][cat3];

I don't wish ref to store the contents of the referenced data with the object, rather the location within its structure. This would allow me to update the Object after some iteration.

Instead of:

Object[cat1][cat2][cat3] = data;

(which I've lost through further iteration)

ref = data;

I'm kinda tying myself in knots and would really like if someone could point me in the right direction. Thanks in advance!

Ladforce · 2 Sep 2008 at 15:24

Could you post your code so we can see what your trying to achieve.

likwid · 2 Sep 2008 at 16:23

If it's not clear from the pseudo code then the actual code won't make things any clearer.

Inquisitor · 2 Sep 2008 at 17:23

It depends whether the data being stored there are value types or reference types. If they're reference types then the code you posted will work, but if they're value types then you'd need pointer semantics, which JavaScript doesn't have.

Ladforce · 2 Sep 2008 at 17:28

Inquisitor said:
It depends whether the data being stored there are value types or reference types. If they're reference types then the code you posted will work, but if they're value types then you'd need pointer semantics, which JavaScript doesn't have.

Yep, youd have to make a copy of the object and then take the data out you need.

likwid · 2 Sep 2008 at 17:31

Ah ok. Cheers guys!

likwid · 3 Sep 2008 at 11:09

So still having this problem. Is there an alternative?

For example, it would be convenient if I could do this:

Code:

function objBuild (someIds){
  var st = '';
  for (var i in someIds){
     st = st + "[" + someIds[i] + "]";
  }
  obj+someIds = newData;
}

But of course this obj+someIds results in a string, rather than a reference to an object within an object, or object of object of object etc.

Alternately I considered:

Code:

function iter(obj, selCats, data){
  for (var x = 0; x < obj.length; x++){
    if (obj[x].id==selCats[x]){
      iter(obj[x], selCats, data);
      break;
    } 
  }
  obj[selCats[x]] = data;
}

But this would leave the original object untouched.

If this isn't clear please let me know and i'll try explain better.

SimonCHere · 3 Sep 2008 at 11:28

Can't you Eval the string and store the data into it?

eval(obj+someIds) = newData;

No idea if it will work but there you go!

likwid · 3 Sep 2008 at 11:47

Sounds good but I get 'missing ] after element list' and can't figure out how to fix it.

Ladforce · 3 Sep 2008 at 14:14

I dont think how you are doing it will work, you need to make a new object to store the old data in so you can modify the first object and still have a copy of the old data.

Code:

  function copy_object( objectToCopy )
  {
    var newObject = new Object();

    for ( var element in objectToCopy )
    {
      newObject[element] = objectToCopy[element];
    }
    return newObject;
  }

likwid · 3 Sep 2008 at 14:36

Thanks for that!

Looks great. I think it needs some modification to work recursively but should be me on the right track. Cheers!

Ladforce · 3 Sep 2008 at 15:51

Yep it wont work for objects of objects but for a single object it will be fine