jQuery.on() selector should only apply to descendants of the element

[contact@…]

The $.on() method accepts a CSS selector parameter in order to setup delegated event handlers.

According to the documentation, this selector only applies to descendants of the element :

A selector string to filter the descendants of the selected elements that will call the handler. If the selector is null or omitted, the handler is always called when it reaches the selected element.

The current implementation when the event is triggered via jQuery.event.dispatch is to call $.is() in order to match the event.target and its parents. The issue with $.is() is that it will not only test for descendants, but also for parents of the element. Considering the documentation, I think this is unintuitive.

Below an example of the issue : JSBin link : ​http://jsbin.com/ocijif/1/embed?live

[Julien Huang <contact@…>]

Github Pull Request : ​https://github.com/jquery/jquery/pull/906

[gibson042]

This is working as designed. If you want the thead in your filtering selector to be a descendant of the context element, specify it accordingly: ​http://jsbin.com/ocijif/2/edit

[scottgonzalez]

It may be working as designed, but isn't this just as bad as qSA?

[dmethvin]

Actually I thought I had fixed this in 1.8.0 so it's worth another look. I'm mobile ATM so I will do this later.

[dmethvin]

I did fix the issue in 1.8.0, but only for positional selectors like :first where .is() already uses the exact same code being proposed by the pull request.

What I wonder is, should $(selector, context).is(selector) always be rooted at context as well? At the moment, it is not unless the selector is a positional one.

@timmywil I know we discussed this when the change for positionals was made but I don't recall all the details.

​https://github.com/jquery/jquery/commit/70e2e32e0eb03607ad0c8b7752dbd7747da47164

[gibson042]

Replying to dmethvin:

What I wonder is, should $(selector, context).is(selector) always be rooted at context as well? At the moment, it is not unless the selector is a positional one.

I would vote against that. There is an argument to be made for the restricted context when it is obvious (as in the case of .on(events, selector, handler)) or necessary (as in the case of positionals). But if we make it universal, then functions accepting jQuery object parameters won't be able to trust .is("ancestor *") because the objects might have been constructed with a context descended from ancestor.

[dmethvin]

It *does* seem rather obscure if the context gets too far away from the .is(). It seemed worth making the exception for positionals because people are constantly confused by the case mentioned in the code.

[timmywil]

I agree with @gibson042. Makes sense for .on(), but not .is(). .is() shouldn't be context dependent. The set is already limited and may contain elements from all over the page. Limiting matching to a particular context would produce unexpected results.

[Dave Methvin]

Fix #12383. All selectors should be delegateTarget-relative

Changeset: afd717df9e189d3e374ce938f03e2712f31c29e3