Question

Does creating and reusing a reference increase performance appreciably when the selector is $(this)?

I create references for my jQuery selectors when I use the same selector multiple times in the same scope. The following is more efficient

    var jSel = $('div.some_class input.some_other_class');
    some_function1(jSel);
    some_function2(jSel);

than this

    some_function1($('div.some_class input.some_other_class'));
    some_function2($('div.some_class input.some_other_class'));

But what if the selector is simply $(this) where this is a dom element inside a jQuery method. Should I bother to create a reference to $(this) and reuse the reference or can I create multiple $(this) selectors and expect similar performance?

Is the following

    var jSel = $(this);
    some_function1(jSel);
    some_function2(jSel);

significantly faster than the following?

    some_function1($(this));
    some_function2($(this));

Answer 1

Is the following significantly faster than the following?

No. It is microscopically faster; in the realms of just a few microseconds.

Does that stop you assigning the result to a variable and using that? No. Using a variable can give more meaning to what this is, and can be easier to type. Plus, if you stopped wanting to operate on $(this), and instead wanted $(this).next(), you have to change it in one place instead of n.

You’ll find the jQuery constructor is highly optimized for accepting a single DOM element as a parameter. The following is the exact code that gets executed when you call $(DOMElement) (after the jQuery object has been created, of course):

var match, elem, ret, doc;

// Handle $(""), $(null), or $(undefined)
if ( !selector ) {
    return this;
}

// Handle $(DOMElement)
if ( selector.nodeType ) {
     this.context = this[0] = selector;
    this.length = 1;
    return this;
}

// Handle lots of other param types, but we hit the above one, so we've stopped now...