What is the relative performance of the pseudo-class and custom selectors?

Question

I understand that in terms of selector speed, these #ID selectors are the fastest, and then the element selectors, and then the .class selectors.

I always assumed that pseudo-class selectors and custom selectors (those in the form of ': selector') are like .class selectors, but I realized that I'm just not sure.

I understand that this depends on the complexity of the code inside the pseudo-class / user selector, so I think I would like to know the answer with this excluded as a factor.

Any help would be appreciated.

Thanks.

Answer 1

It all comes down to what methods in the DOM engine Sizzle (which jQuery uses to evaluate selectors) can use to search for elements.

It can use the getElementById and getElementsByTagName methods to quickly get items for a specific identifier and for a specific tag name. After that, he just needs to go through all the elements found and compare them with the conditions created from the selector.

Methods in the DOM can be used for any element and used in combination, so, for example, finding all div elements inside an element with a specific identifier is very fast.