adding object on array updates previous object

Question

I have a problem regarding putting objects on array. I'm doing this for recording the history of the activity so I store every object on an array by pushing it inside. but when I push it the previous object data is updated with the current. I don't know where the problem is? I really need help in this. Thank you.

I've tried to clone the object by this:

function deepCopy(obj) {
if (Object.prototype.toString.call(obj) === '[object Array]') {
        var out = [], i = 0, len = obj.length;
        for ( ; i < len; i++ ) {
            out[i] = arguments.callee(obj[i]);
        }
        return out;
    }
    if (typeof obj === 'object') {
        var out = {}, i;
        for ( i in obj ) {
            out[i] = arguments.callee(obj[i]);
        }
        return out;
    }
    return obj;
}

but still no luck in here. :(

Code is missing

Prasath K
– Prasath K

2013-05-07 10:25:13 +00:00
Commented May 7, 2013 at 10:25 — Prasath K
– Prasath K, Commented May 7, 2013 at 10:25
Please show your code.

Aleks G
– Aleks G

2013-05-07 10:25:47 +00:00
Commented May 7, 2013 at 10:25 — Aleks G
– Aleks G, Commented May 7, 2013 at 10:25

Guffa · Accepted Answer · 2013-05-07 10:30:09Z

2

The problem is most likely that you are pushing the same object over and over. Example:

var obj = {};
var arr = [];
for (var i = 0; i < 10; i++) {
  obj.index = i;
  arr.push(obj);
}

The result is an array with ten references to the same object.

You have to create a new object instance each time. Example:

var arr = [];
for (var i = 0; i < 10; i++) {
  var obj = {};
  obj.index = i;
  arr.push(obj);
}

The result is an array with ten references to ten separate objects.

answered May 7, 2013 at 10:30

Guffa

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5 Comments

rjx44 Over a year ago

tnx for the quick response @guffa. I think you have pointed out the problem. But is it possible to copy the current object and just set it to a new object?

Guffa Over a year ago

@rjx44: You would do that by creating a new empty object, and copy all properties from the original object. Usually it's easier to just create another instance of the original object.

rjx44 Over a year ago

I've pasted the code for copying but still it changes the previous data.

Vincent McNabb Over a year ago

If you're using jQuery, you can simply go, var copy = $.extend({}, original);

Guffa Over a year ago

@rjx44: Note that cloning like that is shallow. If your object contains any objects or arrays, you have to clone those also to make a deep cloning.

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