Feature request: allow ngEvents to opt out of $apply

[chrisirhc]

Right now, assigning ngEvent directives such as ngClick or ngMouseenter on an element causes it to always call apply when those events are triggered. This can be a huge performance issue if you have ngMousemove on a large element in a large application. It'll trigger $apply continuously which makes it almost unusable. There are also cases where a developer wants to listen to some events (and only trigger certain expressions) only under certain conditions instead of all the time.

I suggest a function that can opt out of $apply which could be useful for developers who want to trigger $apply only when it's needed.

This could come in the form of a local function such as $shouldApply, where the user can call $shouldApply(false) in their expression. Or it can simply follow the preventDefault convention by having a $preventApply() function. I don't think it should use the event.preventDefault to determine not to $apply though, since that maybe used for other purposes by the developer.

[shahata]

#8301 solves this issue

[dragosrususv]

+1
Interesting approach.
We had to implement a feature where hovering a row in a table would update a gantt chart below it and had to implement our own mouse-enter and mouse-leave directives and trigger local $digests (lots of global $digests were triggered via default ng-mouse* directives when quickly moving the mouse up and down and the gantt chart was displaying the update info with a big delay).

[btford]

@chrisirhc I feel like you're better off writing your own directive for these cases. I don't think you want so many details that affect the correctness of your app lurking in your template.

[dragosrususv]

@btford : Hijacking default digests in AngularJS seems like a big step.

Still, I think what @chrisirhc is actually trying to achieve is drag&drop. Since AngularJS is html enhanced, I don't see any reasons why it wouldn't allow users to drop this digest (at developer's risk and expense) on sensitive events like mouse-* or scroll - not by implementing their own (you know this, but jun-mid devs do not), but within the framework itself.
A warning could be added in the documentation regarding this sensitive feature and it's purpose.

my2c

[wesleycho]

I looks like #8301 was rejected - is this feature request rejected then?

[dragosrususv]

Weird indeed. I proposed another API for this in #8301 , but the first one would have been ok too -- as long as there's something that helps us out.