Check array for multiple values in specific order

Question

I have this array (below) and I'm trying to check if it has specific values.

var a = [ true, "lipsum" ];

What I need to do, is to check if a[0] is true and if a[1] is "lipsum"

I could check both values separately:

a[0] === true && a[1] === 'lipsum' // true

...to shorten the code a bit, I tried to do this:

a === [ true, 'lipsum'] // false

Why is this code example above false and is there another way to achieve what I'm trying to do?

I could do this:

a.join() === 'true,lipsum' // true

though I can't help but feel that there is a better way..?

jsfiddle

mVChr · Accepted Answer · 2013-02-14 00:11:01Z

1

For only two elements to check the straightforward way seems best, but I assume you want to do this for maintenance reasons because eventually you may have several conditions to check (not just two). If so, you can do something like the following, which seems verbose for only two conditions, but as you start adding more it would be more reasonable, so here's an example with 5 conditions to check:

// set a constant somewhere for your truth condition
var COND = [1, 'a', 5, 'b', 0];

// check `a` against the constant array using `every` (Thanks Bergi)
if (a.every(function(v, i){ return COND[i] === v; })) {
    // all array elements the same
}

edited Feb 14, 2013 at 0:11

answered Feb 14, 2013 at 0:00

mVChr

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1 Comment

Bergi Over a year ago

Use every() instead of filtering and comparing lengths

Explosion Pills · Accepted Answer · 2013-02-13 23:53:20Z

0

Each array is a separate object, so the equality operator cannot be used to compare them. Assuming that you have a strict comparison of known arguments to do, the first method you use is the best.

If you have another array of arguments that the original array must contain, you must use a loop, although you could abstract it:

Array.prototype.contains = function (array) {
    for (var x = 0; x < array.length; x++) {
        if (this.length < x || this[x] !== array[x]) {
            return false;
        }
    }
    return true;
}

http://jsfiddle.net/q5DvG/1/

answered Feb 13, 2013 at 23:53

Explosion Pills

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7 Comments

Joonas Over a year ago

I ran a jsperf to see how much .join would slow it down, which isn't that much... jsperf.com/array-vs-string123456789 ...but I figured that it isn't worth it and went with checking each one separately.

Explosion Pills Over a year ago

@Joonas .join will coerce elements to strings and your strict comparison will no longer make sense.

Joonas Over a year ago

I don't see how it wouldn't make sense?

Explosion Pills Over a year ago

@Joonas [true].join() !== true

Explosion Pills Over a year ago

@Joonas I think there's a bit of a disconnect here .. comparing to static values known by you is small potatoes. You can write whatever you want. If you had to deal with variables, you could run into trouble if it was unclear what was coming in: true vs. "true"

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