Javascript: what lookup is faster: array.indexOf vs object hash?

Question

I have to perform a LOT of lookups, while parsing xmlStream if i need some tag or not.

I can do it with array.indexOf method (i have about ~15 items in array) or using object[key] lookup.

Second solution seems more efficient in theory for me, but does not look line nice in my code. But if it is really more efficient, i would leave it as it is.

E.g.:

var tags = [
    'tag1',
    'tag2',
    'tag3',
    ...
];

var tags2 = {
    'tag1' : null,
    'tag2' : null,
    'tag3' : null,
}

tags.indexOf(value) // exists?
tags2[value] // exists?

I'd say chose the structure that makes the most sense. 15 items is nothing, it won't be noticeable, you risk making the code hard to read for no apparent benefit. — elclanrs, Aug 26 '15 at 19:11
in understandable language lookup in hash takes constant time and indexOf is linear time. — Maytham Fahmi, Aug 26 '15 at 19:26

score 62 · Answer 1 · edited Jun 20 '20 at 09:12

62

Object key lookup is faster than Array.indexOf(). You can check it on jsperf.

Test Results:

Array

Index of 10000 items: 26,547 Operations/sec
Index of 100000 items: 2,493 Operations/sec

Object

Lookup key of 10000 items: 152,115 Operations/sec
Lookup key of 100000 items: 150,450 Operations/sec

edited Jun 20 '20 at 09:12

Community

1
1

answered Dec 30 '17 at 05:50

StefansArya

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That is significant. Thank you for linking to the test – ow3n Jun 04 '20 at 18:56

score 19 · Accepted Answer · answered Aug 26 '15 at 19:21

Well, the performance depends on your set size and your access pattern. In general, the indexOf is O(n) and hash is O(1), however, since you only have about 15 items in the set and let's say each access is completely independent and equiprobable, the advantage of hash isn't really there.

Javascript: what lookup is faster: array.indexOf vs object hash?

2 Answers2

Array

Object

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