Use the public on method when listening

[jridgewell]

Fixes #3611.

This uses a private listening var to share state between a Backbone
"listener" and "listenee", instead of using a private internalOn() to
share state. This allows #listenTo to use the public #on method and
keeps interop between Backbone and any other event library.

http://jsperf.com/internal-listening-public-on

[megawac]

Why is this necessary - won't it be gced anyway

[jridgewell]

It's now a private global.

[jridgewell]

Hold off on this for today, it has an issue because the other library won't update listening.count, so we don't know when we can cleanup references to listenee from the listener.

[jashkenas]

"The other library" ?

Also, tryCatchOn isn't a good thing.

[jridgewell]

I've just revised the implementation to use a hybrid approach between #3455 and #3594.

If the listenee is using Backbone's #on, the listening will keep track of callbacks using a fast counter (#3594's approach). If not, then callbacks will be stored in an _events object on the listening object (#3455). This allows full interoperability while also properly cleaning up memory bindings when all callbacks have been removed.

JsPerf tends to like the implementation, except Chrome doesn't like #listenTo (running the same benchmark in node v0.12 shows a less than 0.2% slowdown).

---

Also, tryCatchOn isn't a good thing.

Can you explain?

[DomBlack]

Is there any chance this PR will be merged?

[alexbaumgertner]

@DomBlack +1
I'm also interested in this issue. This PR could fix at least one bug in my project.
(Simple demo: http://jsbin.com/yubuhe/6/edit?html,output)

@jridgewell Do you need any help?

[alexbaumgertner]

@jridgewell I tried to rebase and fix merge errors in #4043 but a bunch of tests fails. Could you help me?

[jbboehr]

Any updates on this? I've merged master into it in #4131, if that helps at all.