How do I set the value of another variable to that of an array?

Question

I'm unsure what the problem is here, but here is my code

var btotal = [];
var songarray = [];
function whileplaying() {
    var playingSound = soundManager.getSoundById('aSound');
    for (var i=0;i<8;i++) {
        var ttotal = 0;
        for (var n=0;n<32;n++) {
            var eblock = (i*32)+n;
            ttotal = ttotal+(playingSound.eqData.left[eblock]*100);
        }
        ttotal = ttotal/32;
        btotal[i] = ttotal;
    }
    console.log(btotal);
    songarray.push(btotal);
}

To explain, while the sound is playing I get an array with a length of 8, summing up the EQ values of that frequency block. At the end I append this array to songarray, so the theory is that songarray is an array containing the sound's EQ data in arrays.

The problem is that when I then get the value of songarray, it has however many arrays in it that I expected, but they are all identical, and are all what the last data point was, the latest value of btotal.

So this code would run, and console would display (for example):

[42.743750000000006, 2.98125, 0.10625000000000001, 0, 0, 0, 0, 0]
[38.859374999999986, 2.8, 0.09375, 0, 0, 0, 0, 0]
[56.26874999999998, 21.831250000000004, 3.853125, 0.340625, 0, 0, 0, 0]
[46.459374999999994, 19.584374999999998, 1.4, 0, 0, 0, 0, 0]
[38.08125, 11.8, 1.0750000000000002, 0, 0, 0, 0, 0]

However the contents of song array goes like:

0: Array[8]
0: 38.08125
1: 11.8
2: 1.0750000000000002
3: 0
4: 0
5: 0
6: 0
7: 0
length: 8
__proto__: Array[0]
1: Array[8]
0: 38.08125
1: 11.8
2: 1.0750000000000002
3: 0
4: 0
5: 0
6: 0
7: 0
length: 8
__proto__: Array[0]

Which are all the contents of the latest btotal array. This leads me to believe that each entry in songarray merely points to btotal. So how do I make it so that each array in songarray is the value of btotal at the time I append it, and not merely a pointer?

Your playingSound variable is the exact same in every iteration as you set it outside the loop, and never change it. Did you expect it to magically change? — adeneo
– adeneo, Commented Dec 7, 2012 at 0:24
Sorry, I didn't explain that. What it returns is a sound instance in SoundManager, which data can be retrieved from. whileplaying() is called every 50ms — Liam Bigelow
– Liam Bigelow, Commented Dec 7, 2012 at 0:45

Swadq · Accepted Answer · 2012-12-07 00:30:48Z

1

Define btotal within the scope of the function:

var songarray = [];
function whileplaying() {
    var btotal = [];
    var playingSound = soundManager.getSoundById('aSound');
    for (var i=0;i<8;i++) {
        var ttotal = 0;
        for (var n=0;n<32;n++) {
            var eblock = (i*32)+n;
            ttotal = ttotal+(playingSound.eqData.left[eblock]*100);
        }
        ttotal = ttotal/32;
        btotal[i] = ttotal;
    }
    console.log(btotal);
    songarray.push(btotal);
}

answered Dec 7, 2012 at 0:30

Swadq

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1 Comment

Liam Bigelow Over a year ago

Thank you very much, worked perfectly. I'm still fairly new to javascript, intricacies of some things are lost on me.

user1884047 · Accepted Answer · 2012-12-07 00:30:32Z

1

You probably want to copy the array.

Instead of

songarray.push(btotal);

use

songarray.push(btotal.slice(0));

answered Dec 7, 2012 at 0:30

user1884047

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