Object values to array but with same reference

Question

I have an object with dynamic properties. Each of these properties are removed and added based on some events. I want to have a function or property in this object which can return the array of values but having the same reference all the time. Whats the best way to do it?

For e.g if current state of the object is

var obj = {"410f0ec7bd420d6eafea36bedb716ade" : { 'name' : 'dark'} }
var values = obj.someFunction()

values should be [{ 'name' : 'dark'}]

if current state of obj is

{"410f0ec7bd420d6eafea36bedb716ade" : { 'name' : 'dark'} ,
"f44abc3bb1dad3cd20e97e6a21416830": { 'name' : 'magic'}}

values should be [{ 'name' : 'dark'},{ 'name' : 'magic'}]

The reference of the array and the properties should never change (unless they are deleted).

What do you mean by "the reference of the array"? Its address in memory? — Robby Cornelissen, Jun 13 '14 at 12:12
Do you mean `values` should automatically update when `obj` is changed? — Bart, Jun 13 '14 at 12:12
@Bart: Yes, I was doing something like return return Object.keys(obj).map(function (key) { return obj[key] }); But that returns a new array every time — Pradeep Mahdevu, Jun 13 '14 at 12:17
And you want to mix in this method in the data object (`obj`)? — Robby Cornelissen, Jun 13 '14 at 12:26
@PradeepMahdevu You're out of luck unless you want to use `Object.observe` which has very bad browser support, but there's a polyfill available. — Bart, Jun 13 '14 at 12:28

score 1 · Accepted Answer · edited May 23 '17 at 12:05

1

How about this? It maintains the same array. If you want, you could also mix it in with the object, but would have to add a guard to not also add the function to the values.

var values = someFunction(obj, values);

function someFunction(obj, values) {
    values = values || [];
    values.length = 0;

    for(var key in obj) {
        values.push(obj[key]);
    }

    return values;
}

By the way, clearing the array by setting its length to 0 was gleaned from this post.

edited May 23 '17 at 12:05

Community

1
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answered Jun 13 '14 at 12:36

Robby Cornelissen

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The only thing with this approach is that it changes the reference of the objects. – Pradeep Mahdevu Jun 13 '14 at 12:42
The objects in the values you mean? – Robby Cornelissen Jun 13 '14 at 12:44
Yes, each of those references are tied back to view, and i would like to not refresh the array. If i do, its a huge refresh. – Pradeep Mahdevu Jun 13 '14 at 12:47
+1 for the values.length =0 ; but on a general note it is slower. – Pradeep Mahdevu Jun 13 '14 at 12:53
It's an interesting problem, and at this point I'm not really sure if there's a solution that fits all your requirements. I'll try to look into it some more. About the `length = 0` being slower: it seems that looping and popping is indeed the most efficient, but I guess it very much depends on the Javascript engine. – Robby Cornelissen Jun 13 '14 at 12:59
This [script](https://github.com/melanke/Watch.JS/blob/master/src/watch.js) might interest you. It does depend on the browser/engine's internal methods though... – Robby Cornelissen Jun 13 '14 at 13:14

score 1 · Answer 2 · answered Jun 13 '14 at 12:38

1

My might create a 'meta'-object that stores a reference to the original object and can return the values:

var Values = function(obj) {

 this.getValues = function() {

  var values = [];
  for(i in obj)
   values.push(obj[i]);
  return values;
 };

}

var original = {"410f0ec7bd420d6eafea36bedb716ade" : { 'name' : 'dark'} ,
                "f44abc3bb1dad3cd20e97e6a21416830": { 'name' : 'magic'}};

var vals = new Values(original);

var values = vals.getValues();

answered Jun 13 '14 at 12:38

fast

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The only thing with this approach is that it changes the reference of the objects. – Pradeep Mahdevu Jun 13 '14 at 12:41
@PradeepMahdevu With this approach, changes to 'values' actually are reflected in 'original'. – fast Jun 13 '14 at 12:49
When you are calling getValues() each time, you are returning a new array. So the array is a new ref every time. you can get away with that, values = values || []; values.length = 0; – Pradeep Mahdevu Jun 13 '14 at 12:54

score 0 · Answer 3 · answered Jun 13 '14 at 12:14

Given that you seem to be generating the array within "someFunction" (seeing the code of the function and how you attach it to the object would help), you'll need to keep an instance of an array and empty/refill it rather than create a new one. It could be a member of your object (obj.currentItems) or within a closure (depending on how you create it), and it could be updated as you change its properties or on demand within someFunction.

I'll update my answer if you provide more specific code.

Object values to array but with same reference

3 Answers3