Testing on Objects in JS Arrays

Question

I have an array of objects being returned after an API request. It takes the form:

[{
    id: 12,
    slug: '050e8e8db93ae08ed46cd57017ef9617',
    name: 'Test Badge'
}, {
    id: 13,
    slug: '78ed09b1f2aae29ab30915ac9f167bfa',
    name: 'Test Badge'
}]

I need to test for a value: x on the key: slug, but my array of objects is hundreds of objects long. Is there a way to test for a value without looping through all the objects manually?

No there isn't. However, if you have to perform this test multiple times, build a slug -> object map so that you can simply lookup slug. — Felix Kling
– Felix Kling, Commented Jan 12, 2015 at 17:10
Are the objects arriving in any particular order, by slug? If they are, you might be able to perform a binary search. If not you don't have a choice, just loop through them manually. — La-comadreja
– La-comadreja, Commented Jan 12, 2015 at 17:10
possible duplicate of best way to get a specific object from and array without looping — Bergi
– Bergi, Commented Jan 12, 2015 at 17:36

Fuzzyma · Accepted Answer · 2015-01-12 17:30:20Z

3

Well - somehow you have to loop. But at least JavaScript is doin the job for you:

var arr = [
    {
        id: 12,
        slug: '050e8e8db93ae08ed46cd57017ef9617',
        name: 'Test Badge'
    },
    {
        id: 13,
        slug: '78ed09b1f2aae29ab30915ac9f167bfa',
        name: 'Test Badge'
    }
];

var arrWithValue = arr.filter(function(el){ return el.slug === value; });

arrWithValue contains only the elements of the array with the correct value.

When you have to access these data very often it would be better to loop one time and save every object using the slug as key.

var sortedObj = {};
for(var i = 0, len = arr.length; i < len; ++i){
    sortedObj[arr[i].slug] = arr[i];
}

// access the object with sortedObj['someSlug']

edited Jan 12, 2015 at 17:30

answered Jan 12, 2015 at 17:13

Fuzzyma

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1 Comment

Scott Sauyet Over a year ago

Good answer overall. I'd suggest not using for-in on arrays, though.

agershun · Accepted Answer · 2015-01-12 17:34:23Z

0

Question: do you need filter or test array for value? If test, then it is better to use some() function.

Update: According jsPerf http://jsperf.com/json-stringify-vs-array-loop some() faster in 800 times then filter() and 5000 then JSON.stringify.

    var data = [{
        id: 12,
        slug: '050e8e8db93ae08ed46cd57017ef9617',
        name: 'Test Badge'
    }, {
        id: 13,
        slug: '78ed09b1f2aae29ab30915ac9f167bfa',
        name: 'Test Badge'
    }];

    function test(x) {
        return data.some(function(d){return x==d.slug});
    };

    console.log(test('78ed09b1f2aae29ab30915ac9f167bfa'))

edited Jan 12, 2015 at 17:34

answered Jan 12, 2015 at 17:14

agershun

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2 Comments

Spencer Wieczorek Over a year ago

the function .some() will still iterate through the array.

agershun Over a year ago

According jsPerf jsperf.com/json-stringify-vs-array-loop some() faster in 800 times then filter() and 5000 then JSON.stringify.

agershun · Accepted Answer · 2015-01-12 17:38:30Z

0

Another "non-iterating" option (it is possible here because your key is very specific), but this is slowest because JSON.stringify is slow operation:

function test(x) {
    return JSON.stringify(data).indeхOf(x) > -1;
}

edited Jan 12, 2015 at 17:38

answered Jan 12, 2015 at 17:19

agershun

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