Which JavaScript function is faster

Asked Sep 02 '15 at 20:23

Active Sep 02 '15 at 20:23

Viewed 185 times

As I progress to teach myself JavaScript, an aspect comes to mind. Which function is faster and uses less memory of finding id's in an html?

I see this function very often but I've never used it:

document.getElementById("abc");

I use this everywhere in my Polymer app:

document.querySelector('#abc');

I hope I have not asked a silly question but few weeks ago I was reading an article and someone mentioned one is faster. Could someone explain if this is true please?

asked Sep 02 '15 at 20:23

Sylar

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Measure it and find out. – Tripp Kinetics Sep 02 '15 at 20:25
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no way to tell, as it'd depend on the particular JS engine you're using. You'll have to test it. – Marc B Sep 02 '15 at 20:25
@MarcB how do you test/measure it? – Sylar Sep 02 '15 at 20:25
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This is pretty cool worth a peak https://jsperf.com/jquery-selectors-vs-native-api – vikingben Sep 02 '15 at 20:26
you benchmark it. do a bunch of selections and time how long they take, and do enough of them for long enough that random background system "noise" doesn't throw off the results. – Marc B Sep 02 '15 at 20:26
@vikingben actually that's not a jQuery selector, it's the native .querySelector – Jack Sep 02 '15 at 20:27
@Jack hmm I thought they were all there my bad. Still think it's worth a peek. – vikingben Sep 02 '15 at 20:29
`document.getElementById` seems to be the fastest – Sylar Sep 02 '15 at 20:30
@vikingben the test you linked does not include the case the OP is asking for. – Dave Sep 02 '15 at 20:30
@dave that link does compare the speed of the two functions mentioned by OP – hopkins-matt Sep 02 '15 at 20:31
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https://jsperf.com/getelementbyid-vs-queryselector – Bitwise Creative Sep 02 '15 at 20:31
@hopkins-matt no it doesn't. It doesn't use a querySelector by id – Dave Sep 02 '15 at 20:32
Marked as duplicate. Where is the original question as I need to know? – Sylar Sep 02 '15 at 20:33
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@dave ah. you are correct. overlooked that the test used class. – hopkins-matt Sep 02 '15 at 20:33

Which JavaScript function is faster

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