Strange console output array and array.pop() in javascript function

Question

Possible Duplicate:
Is Chrome's JavaScript console lazy about evaluating arrays?

I write next js function:

function popFromArray(arr){
    console.info(arr);
    console.info(arr.pop());
    console.info(arr);
}

When I write next code in console I expected next output:

>>> popFromArray([12, 432, 52, 523]);
[12, 432, 52, 523]
523
[12, 432, 52]

But I found strange behaviour for me (chrome and firefox):

>>> q = [12, 432, 52, 523];

>>> popFromArray(q);
[12, 432, 52, 523]
523
[12, 432, 52, 523]

>>> popFromArray(q);
[12, 432, 52]
523
[12, 432, 52]

>>> popFromArray(q);
[12, 432]
52
[12, 432]

Is anybody can explain why it happens?

score 2 · Accepted Answer · answered Feb 20 '12 at 06:43

2

Try to step over through the function code: it will report properly.

I think it's just a concurrency issue. Console output generation is done in parallel with program execution so result is unpredictable.

answered Feb 20 '12 at 06:43

Dmitry Nogin

3,670
1
19
35

score 0 · Answer 2 · answered Feb 20 '12 at 07:17

This is the intended behavior of pop(), according to the MDN pop() will:

Removes the last element from an array and returns that element.

To realize your intention, you should try

function popFromArray(arr){
    console.info(arr);
    console.info(arr[arr.length -1]);
    console.info(arr);
}

Strange console output array and array.pop() in javascript function

2 Answers2