Javascript Array delete or pop causing race condition with console.log?

Question

On the current Google Chrome (Version 22.0.1229.79, on an iMac with Mountain Lion), the following code

var arr = [1, 3, 5];
console.log(arr);

delete arr[1];
console.log(arr);

console.log(arr.pop());
console.log(arr);

will show

[1, undefined × 2] 
[1, undefined × 2] 
5 
[1, undefined × 1]

there are also other situation that caused Firefox to behave similarly as well. Are they bugs on Chrome and Firefox -- but it would seem strange that both Firefox and Chrome are susceptible to similar bugs -- or is it some behavior with array delete and console.log? Supposedly, console.log should not be running on a separate thread.

possible duplicate of Is Chrome's JavaScript console lazy about evaluating arrays? — Felix Kling
– Felix Kling, Commented Oct 7, 2012 at 9:13
@動靜能量: Seems like a bug that was done by the same person. FF14 is fine, while FF15 is not. Vandalized? — Jay
– Jay, Commented Oct 7, 2012 at 9:29

XiM · Accepted Answer · 2012-10-07 08:16:29Z

1

In Firefox 7.0:

var arr = [1,3,5];

console.log(delete arr[1]); // will show [1, undefined, 5]

And in my opinion it's a correct behavior =) So may be it's just a bug.

answered Oct 7, 2012 at 8:16

XiM

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3 Comments

xdazz Over a year ago

The op is not asking why the result is [1, undefined, 5].

nonopolarity Over a year ago

a similar bug showed up on Firefox 15.0.1 but it involved 10 tests for arr1 to arr10, and if I removed the test for arr9, then the output became "correct", and if I removed the test for arr1 to arr8, the output became "correct" again. arr10 is totally independent of other array tests, so it is similar to what Chrome was showing in the original question

XiM Over a year ago

So delete is working correct and console.log isn't. If you do not re-define the console.log, I would suggest that this is simply a bug of browsers.

Community · Accepted Answer · 2017-05-23 10:24:54Z

1

It is due to queued up console.log processing, so the printing is delayed, and it shows a later version of the object or array: Is Chrome's JavaScript console lazy about evaluating arrays?

My answer there has 5 solutions and JSON.stringify() was the best one.

edited May 23, 2017 at 10:24

CommunityBot

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answered Oct 9, 2012 at 16:06

nonopolarity

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