redefining array push method in javascript?

Question

I'm newbie in js. I redefined push() method in Array Object like below..

Array.prototype.push = function(item) {
    this[this.length] = '[' + item + ']';
    return this;
};

var arr = new Array();
arr.push('my');
console.debug(arr);
console.debug(arr[0]);

arr.push('name');
console.debug(arr);
console.debug(arr[1]);

arr.push('is');
console.debug(arr);
console.debug(arr[2]);


// output

[] --> <1>
[my]
[] --> <2>
[name]
[] --> <3>
[is]

but I can't understand why <1>,<2>,<3> is empty.

Are you debugging in chrome by any chance? See stackoverflow.com/questions/4057440/… — Crescent Fresh
– Crescent Fresh, Commented Mar 25, 2011 at 2:44

alex · Accepted Answer · 2011-03-25 02:51:22Z

1

If you remove the brackets being concatenated, it works.

jsFiddle.

It looks like push is called internally a bit, and this may be why it is not working.

Also, there shouldn't be any reason to re-implement push yourself.

edited Mar 25, 2011 at 2:51

answered Mar 25, 2011 at 2:46

alex

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3 Comments

user236139 Over a year ago

I too noticed this. Extremely odd behavior.

KJYe.Name Over a year ago

it appears to happen only in webkit browsers.

tbranyen Over a year ago

This does not seem to be the case for me. I justed tested in Chromium 10.0.648.133 (Linux) and the issue is still prevalent.

brainjam · Accepted Answer · 2011-03-25 03:45:56Z

1

Try using console.debug(arr.join(',')); instead of console.debug(arr);.

As in this jsfiddle.

The output is now

[my]
[my]
[my],[name]
[name]
[my],[name],[is]
[is]

Tested on Chrome.

As for the strange behavior of debug.console() when printing arrays, I suspect that it also uses push() on arrays while building the output string. If, for example, you replace the '['+item+']' with '<<'+item+'>>' you get some whackiness in the Firebug console, as in this jsfiddle.

edited Mar 25, 2011 at 3:45

answered Mar 25, 2011 at 2:55

brainjam

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1 Comment

tbranyen Over a year ago

This is a very informative post and most definitely the answer. Chrome Tools wackiness.

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