jQuery selector vs filter()

Question

Given the following markup

    
first item
    ​
second item
    
t         


        

Answer 1

The first is faster:

$("ul li.item")

This is true simply because it's equivalent, but isn't running the selector engine (Sizzle) twice to get there.

For your edit: You use .filter()...well, when you need to filter the current set, or when you need a complex filter. For example if you wanted to chain but not select the set again:

$("ul li").addClass('everyItem').filter('.item').fadeOut();

Or a complex filter:

$("ul li").filter(function() {
  return $.data(this, 'hasSomething');
}).fadeOut();

There are many uses of filter, it really depends on the situation as to what fits best. As pertains to your question though, $(selector).filter(selector)...I can't think of a case where you'd want this over a single selector if it's at all possible. The only case off the top of my head you can't do that is a complex :has() and :not() wrapping.