Why doesn't [a, b, c] == [a, b, c]

Question

Have been bug testing for about 2 hours now only to realise that if two arrays are the same. The logical operator == and === say it isn't.

Firstly, why. Secondly, how can I get this to be true?

Ohh. I see. They have the same value, but are different lists technically — Mathias, Mar 03 '21 at 18:13
Object comparison is not based on the values in the objects; it's based on the basic identity of the objects. — Pointy, Mar 03 '21 at 18:13

score 1 · Answer 1 · answered Mar 03 '21 at 18:15

1

Array is a reference data type, and can never be equal. You can check and compare the data inside both arrays, without shell

answered Mar 03 '21 at 18:15

Yuliia

21
2

Not really.. You can compare the same array to the same array by using a variable as reference to it. – GottZ Mar 03 '21 at 18:23
Ok, you're right. I considered the option as in the example, without a variable – Yuliia Mar 03 '21 at 18:25
Comes in handy if you compare a reference against members of an array that contains arrays. even indexOf etc. work in that case. – GottZ Mar 03 '21 at 18:26
Commonly used in caching / pooling / queueing – GottZ Mar 03 '21 at 18:27

bartholomew · Accepted Answer · 2021-03-03T18:21:25.773

0

Try this:

JSON.stringify(array1) == JSON.stringify(array2)

You're using logical comparisons between values, not for arrays/objects. Alternatively you can:

if (array1.length == array2.length){
    for(var i = 0; i <= array1.length; i++){
        if(array1[i] != array2[i]){
            return false;
        }
    }
    return true;
} else {
    return false;
}

edited Mar 03 '21 at 18:21

answered Mar 03 '21 at 18:16

bartholomew

102
8

1

doesn't always work. E.g. if it's arranged differently – Keimeno Mar 03 '21 at 18:16
This would fail if the members are in a different order – old greg Mar 03 '21 at 18:16
While technically correct, it's a terrible way to do so because 1) it's slow, 2) `array1` or `array2` may have circular dependencies, 3) order needs to e preserved/normalized. – Zepplock Mar 03 '21 at 18:18
Also not all arrays can be stringified like that – Pointy Mar 03 '21 at 18:18
OP asked for comparison between [a,b,c] == [a,b,c] not [a,b,c] == [c,b,a] or anything related to complex datasets. – bartholomew Mar 03 '21 at 18:26

Why doesn't [a, b, c] == [a, b, c]

2 Answers2