Question

Reguarding jQuery, I’ve read somewhere that slecting by class can be significantly slower than selecting by ID.

When using the :first selector, does jQuery find all instances and only return the first element? Or does the parser stop once the first element is found?

Answer 1

I know this isn’t a direct answer to your question but:

Using .first() is about ten times faster than using :first. Tested using Firefox

100,000 iterations:

55,870ms using :first

5,858ms using .first()

$(document).ready (function() {
    var i, time = +new Date;
    for ( i = 0; i < 100000; ++i ) {
        $ ( 'div:first' );
    }
    console.log ( (+new Date) - time );

    time = +new Date;
    for ( i = 0; i < 100000; ++i ) {
        $ ( 'div' ).first ( );
    }
    console.log ( (+new Date) - time );
});

As the comments have suggested, try using JsPerf