Question

I’m doing very frequent iterations over arrays of objects and have been using jQuery.each(). However, I’m having speed and memory issues and one of the most called methods according to my profiler is jQuery.each(). What’s the word on the street about its performance? Should I switch to a simple for loop? Of course I’m fixing the many issues in my own code too.

Answer 1

The source code for jQuery’s each is as follows (Thank you John Resig and MIT License):

each: function( object, callback, args ) {
    var name, i = 0, length = object.length;

    if ( args ) {
        if ( length === undefined ) {
            for ( name in object )
                if ( callback.apply( object[ name ], args ) === false )
                    break;
        } else
            for ( ; i < length; )
                if ( callback.apply( object[ i++ ], args ) === false )
                    break;

    // A special, fast, case for the most common use of each
    } else {
        if ( length === undefined ) {
            for ( name in object )
                if ( callback.call( object[ name ], name, object[ name ] ) === false )
                    break;
        } else
            for ( var value = object[0];
                i < length && callback.call( value, i, value ) !== false; value = object[++i] ){}
    }

    return object;
}

As you can trace and see, in most cases it is using a basic for loop where the only overhead is really just the callback itself. Shouldn’t make a difference in performance.

EDIT: This is with the realization that selector overhead has already occurred and you are given a populated array object.