Fixing $.proxy to work like (and use) Function.prototype.bind

[gf3]

As it stands currently, $.proxy is in a weird place. It's likely too advanced of a tool for the average user, and crippled for advanced users. It lacks the ability to partially apply arguments and doesn't take advantage of native implementations where available. As well, $.proxy is being used internally to set matching guids (in $.fn.bind and $.fn.toggle), which is an unnecessary performance hit as well as reliance on an indirect side-effect of $.proxy.

My proposal is to:

• Make $.proxy spec-compatible.
• Use native implementations where available.
• Remove the non-standard object/key syntax (breaking).

[gf3]

I've committed a fix which takes care of the following:

• Makes $.proxy spec compatible.
• Uses native Function#bind where available.
• Removes the non-standard object/key syntax.
• Fixes locations where $.proxy is being used incorrectly internally.
• Added tests to support new functionality.

The bind fallback I used is based on research from the ​Prototype bug tracker and is ultimately by Juriy Zaytsev (@kangax).

Native bind is used where possible, which is ​over twice as fast as jQuery's current solution in Chrome 9.

The non-standard object/key syntax has been removed. Yes, this is a breaking change, however it is trivial to use the proper syntax. It adds unnecessary complexity for virtually zero gain.

Internally jQuery was using $.proxy only to set matching guides on related functions. This caused unnecessary overhead. And is just plain wrong. I've fixed this (which I would label as an actual bug).

Patch is on github, a pull-request can be made: ​https://github.com/gf3/jquery/commit/9f8cd6c499844451468257140e71f611abb3a040

[ajpiano]

I am fully in favour of this landing - partial application is worth it alone, and I agree - the stringy syntax is really not necessary and kinda feels yucky, so I am not averse to losing it. If people have used it in the past year since 1.4 came out, I think we can guide them toward the proper syntax...

What do other people think about this for 1.5?

[snover]

I’m not sure what the project’s outlook has been with regards to removing things outright like that in a new version without deprecating it for a release.

(Unrelatedly, I also kind of feel like the method signature should be (thisObj, fn, args…) since that matches other functions that rebind this like Function.call and Function.apply, but that probably won’t happen since it is an even more extreme bc break.)

[Rick Waldron]

Back when this was in discussion on the jQuery Core google group, I had argued the same points - and ultimately $.proxy was the outcome - so I'm gladly in favor of this change, I also think (thisObj, fn, args…) should be used - the function def would have to be nasty overloaded with ugly argument manipulation.

[gf3]

Replying to rwaldron:

Back when this was in discussion on the jQuery Core google group, I had argued the same points - and ultimately $.proxy was the outcome - so I'm gladly in favor of this change, I also think (thisObj, fn, args…) should be used - however the function def would be nasty overloaded with ugly argument manipulation.

Replying to snover:

(Unrelatedly, I also kind of feel like the method signature should be (thisObj, fn, args…) since that matches other functions that rebind this like Function.call and Function.apply, but that probably won’t happen since it is an even more extreme bc break.)

I've followed the style of $.map et al, where the instance which would normally be acted upon is the first argument. E.g.:

ar.forEach( fn ) → $.map( ar, fn )

fn.bind( context ) → $.proxy( fn, context )

fn.bind( context, arg1, arg2 ) → $.proxy( fn, context, arg1, arg2 )

I think if Function#call were implemented in jQuery it would have the following signature: $.call( fn, context, arg1, argN).

[gf3]

Added a commit to add a quick test to $.support for native bind, as per ajpiano's suggestion:

​https://github.com/gf3/jquery/commit/5b1b57850cfd4c92a4f9231581dff7faac489566

[gf3]

Relevant pull request:

​https://github.com/jquery/jquery/pull/133

[gf3]

Added the old syntax back in.

[john]

Landed.

[Rick Waldron]

note that new docs should cover the latest behaviour after the removal of Function.prototype.bind

​https://github.com/jquery/jquery/commit/15da298f72bf94a95563abc12b8e6fec8c604099

[Timmy Willison]

It's ok to have closed tickets that need docs, just add keyword needsdocs.

[Timmy Willison]

#9679 is a duplicate of this ticket.