Does jQuery continue to filter if it finds 0 matches?

Question

I have a question regarding jQuery filtering efficiency. I just wrote a rather long expression, and I was wondering if jQuery would stop filtering if the current number of matches is 0.

passengers.filter('input.FromDate[value="01/09/2011"]') .closest('tr') .filter('input.ToDate[value="08/09/2011"]') .length; 

If after the first call to filter() number of matches is 0, will jQuery continue searching in the DOM or refuse additional calls and just return 0?

Answer 1

The good thing about jQuery chaining is that when there are no matches, nothing bad will happen.

When you call .filter and get null matches, you make calls, followed by a method call by definition, because they are called directly on the returned object (what is a chain).

If there are no matches, JavaScript will still call each subsequent method in each returned object. How much processing will be wasted depends on how the particular method was implemented.

 $.fn.doesItTryToDoStuff = function() { alert('called'); // here I could have some wasteful process // which could foolishly be executed // even when there are no elements return this.each(function() { $(this).css("border", "1px solid red"); }); }; $("input").filter("[value='foo']").doesItTryToDoStuff().doesItTryToDoStuff(); 

Demo version

I would expect most jQuery methods to be encoded in such a way that nothing will happen before the length of the collection is verified, but you never know.

Answer 2

Filtering out what does not exist will return an empty wrapped set. Subsequent filters will be called, but will not have any effect.

 $('div').filter('.isnt-here').end().filter('.spacer').length; 

Running this on the question page returns 25 .

Answer 3

Filtering in jQuery will return a jQuery object with a DOM list of matched elements, a subsequent filter will be called on these DOM elements, etc.

If there are no matches, filtering in jQuery will return a jQuery object with an empty DOM list and will call the subsequent filter for the empty list, so it will not return a match either.

This is similar to narrowing the filter area.