Check if an array contains an array with the same values as a new array

Question

Is there any way to check if an array contains an array with specific values?

Like, I have this array

 drawn[0] = [0,0]

Which I later want to check if still contains [0,0], so I'd do something like

 drawn[0] == [0,0]

But this just returns a false, why? And, more importantly, what should I do instead? Even if I try [0,0] == [0,0] I get a false in return?

Please note that the arrays won't always just be zeros...

Ps. I don't want to use any external libraries, so please keep it to plain ol' javascript

Check the array entries? == will compare the object references, not the contents. — Dave Newton
– Dave Newton, Commented Feb 22, 2013 at 2:12
@FelixKling Oh, I wasn't able to find anything like that... But yea, this is a duplicate then D: — Mobilpadde
– Mobilpadde, Commented Feb 22, 2013 at 2:17

Explosion Pills · Accepted Answer · 2013-02-22 02:15:41Z

4

Everyone's said that you can't compare the arrays because they are objects. That is true. You have several viable solutions including nested loops (either blatantly or abstracted). Others have also suggested this.

A potentially simpler alternative is to compare the the toString values of the two arrays:

drawn[0].toString() == [0,0].toString()

This does require the array contents to be in the same order.

answered Feb 22, 2013 at 2:15

Explosion Pills

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2 Comments

RobG Over a year ago

Since you know what [0,0] will produce as a string, probably better to just compare to 0,0.

Explosion Pills Over a year ago

@RobG I would assume that [0,0] is a variable in the context in which he's using it. It's also safer to use toString() anyway because you don't have to worry about the parsing of the value. For example, You may think [0, 0].toString() is 0, 0, but it's not. It's 0,0.

Ja͢ck · Accepted Answer · 2013-02-22 02:22:48Z

3

Arrays in JavaScript are only equal to one another if they're the same object.

You need to do a contents check instead:

if (drawn[0].every(function(item) { return item === 0; })) {
    // all entries are zero.
}

4 Comments

Decent Dabbler Over a year ago

What is this .all method you speak of? I that standard Javascript? Or pseudo-code perhaps?

Ja͢ck Over a year ago

@fireeyedboy That should be .every() of course, I have my languages mixed up =p

RobG Over a year ago

Worth pointing out that Array.prototype.every is ES5 and therefore not supported by older browsers like IE8.

Ja͢ck Over a year ago

@RobG The link mentioned in my answer also provides the shim.

gdoron · Accepted Answer · 2013-02-22 02:14:12Z

2

Check with a for loop, you can't compare with a simple comparison because it compares the references not the values:

[0]    !== [0]    // true
[0][0] ==  [0][0] //true

answered Feb 22, 2013 at 2:14

gdoron

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Comments

Amadan · Accepted Answer · 2013-02-22 02:13:51Z

0

Objects, including arrays, are compared by object identity. Each time you write [0, 0] you create a new array; so they register as different objects. You would need to iterate yourself through elements and inspect if the elements are the same.

answered Feb 22, 2013 at 2:13

Amadan

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