jQuery select by class VS select by attribute

Question

I want just to ask for an opinion of perfomance: Is it faster selecting elements by class name or by attribute name with jquery? Example I have 100 DIVs element in this form:

<div class="normal_box" normal_box=1>...</div>

Which is faster:

$('div.normal_box').each(function(){...});

VS

$('div[normal_box=1]').each(function(){...});

I made some experiments on 30 divs but I don't see any difference with (new Date).getTime(); Maybe selecting by class is more efficient on CPU usage?

Answer 1

Here is are the results of a test I just ran for myself. This div was on a DOM with 1562 elements.

<div class="banana" data-banana="1"></div>

Tests

    function test(iterations) {

    console.time('query-by-data');
    for(var i=iterations;i;i--) {
        $('[data-banana]');
    }
    console.timeEnd('query-by-data');

    console.time('query-by-class');
    for(var i=iterations;i;i--) {
        $('.banana');
    }
    console.timeEnd('query-by-class');

}

results

 iterations: 1000
 query-by-data: 120.000ms
 query-by-class: 10.000ms

 iterations: 10000
 query-by-data: 1030.000ms
 query-by-class: 56.000ms

 iterations: 50000
 query-by-data: 5151.000ms
 query-by-class: 235.000ms

Answer 2

this is a great post for exactly what you are looking for.

JQUERY SELECTOR PERFORMANCE TESTING

I've also found a great article that may help you on this topic:

• some jquery selectors performance tests

let me know if this answer really helped you, thanks.

update: I've managed to make a sample to match your posted case, here are the results for a total set of 203 divs:

1- by using tag name having certine class name $("div.normal_box") ==> 884 ms

2- by using attribute value $("div[normal_box=1]") ==> 4553 ms

Update 2: I tried even further more than your question, and made it to test a few selectors, here is the new link for this updated test: http://jsfiddle.net/8Knxk/4/

3- by using tag name $("div") ==> 666 ms

4- by using just the class name $(".normal_box") ==> 762 ms

I think it's now more clear for you :)