Question

Which one of the following selectors has better performance, if not the same

1. $('#location_form input#id_name')
2. $('#id_name')

I often have questions like the above pop up in my mind. I can’t really answer them because I lack the knowledge on how selection work behind the scene.

My asks:

1. answer/opinions to the question above
2. references that explain how jQuery selection work behind the scene
3. do all javascript frameworks work in the same way as jQuery when it comes to selection?

Thanks a bunch.

Answer 1

With your selectors, the latter is faster, as jQuery determines you only want to select by ID and returns document.getElementByID: https://github.com/jquery/jquery/blob/master/src/core.js#L145-165

Here is the full source code: https://github.com/jquery/jquery/blob/master/src/core.js#L78-188