weird behaviour of javascript with arrays

Question

Let us consider the following JavaScript snippet

var arr = [];
function pushMe()
{
      var temp = { "name": "me" };
      arr.push(temp)
      console.log(arr)
      temp["name"] = "you";
      arr.push(temp)
      console.log(arr)
}

I was astonished to see the output as [Object { name="you"},Object { name="you"}]

As we are pushing the references, both must refer to same object. But at least after the first push output must be like Object { name="me"}

Why is this happening??

thanks :)

First output comes as [Object { name="me"}] in Firefox, as expected. — Sirko
– Sirko, Commented Dec 7, 2012 at 16:27

Denys Séguret · Accepted Answer · 2012-12-07 16:39:24Z

6

The problem with Chrome's console is that it doesn't copy the objects you pass to it.

By the time Chrome builds the console the objects it displays have changed.

If you want to see your "me", try this :

  var arr = [];
  var temp = { "name": "me" };
  arr.push(temp)
  console.log(arr)
  setTimeout(function(){
      temp["name"] = "you";
      arr.push(temp)
      console.log(arr)
  }, 3000);

and look inside the array in less than 3 seconds.

Fiddle : http://jsfiddle.net/TMDq2/

Some may see it as a bug, some as an optimization. It's at least a borderline implementation...

edited Dec 7, 2012 at 16:39

answered Dec 7, 2012 at 16:25

Denys Séguret

384k90 gold badges813 silver badges780 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Eineki Over a year ago

I was bitten several times from this "feature". If you use the log for debug, in Chrome, it is better to log a json representation of the object or you can miss your issues being overwritten as program goes on.

Collectives™ on Stack Overflow

weird behaviour of javascript with arrays

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related