In general developers should probably default to marking their listeners as passive, unless their listeners are actually going to call preventDefault(). We don't have a console log for saying "use a passive listener", no. We can easily detect listeners that are not marked passive and that are impacting scrolling latency (for example), but it's impossible to tell with 100% accuracy if those listeners *should* be marked passive or not. Some of those listeners are probably legitimately not passive, because they do call preventDefault() under some conditions - but we can't know that until those conditions occur and preventDefault() is called.
Cheers, kats On Thu, May 5, 2016 at 3:21 PM, Justin Dolske <dol...@mozilla.com> wrote: > How will a developer know when it would be worthwhile to mark their event > listener as passive? Do we perhaps log something to the console? > > Justin > > On Wed, May 4, 2016 at 3:19 PM, Kartikaya Gupta <kgu...@mozilla.com> wrote: >> >> Summary: Authors can declare in their addEventListener call that the >> listener will not be calling preventDefault() on the event. This >> unlocks certain performance optimizations. >> >> Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1266066 >> >> Link to standard: >> https://dom.spec.whatwg.org/#dom-addeventlisteneroptions-passive - >> note that this intent email is specifically about the "passive" flag; >> the AddEventListenerOptions dictionary and addEventListener >> modifications were already implemented in bug 1266194. I don't recall >> seeing an intent email for that but maybe I missed it. >> There is also an explainer doc at >> https://github.com/WICG/EventListenerOptions which might be easier to >> read for those already familiar with DOM events. >> >> Platform coverage: all platforms >> >> Estimated or target release: Hoping to get it in Firefox 49. I wrote >> the patches today (they were pretty small) hence combining the intent >> to implement and ship into this email rather than sending two separate >> emails. >> >> Preference behind which this will be implemented: none at the moment >> >> Other browsers: See >> https://github.com/WICG/EventListenerOptions#status-of-implementations >> _______________________________________________ >> dev-platform mailing list >> dev-platform@lists.mozilla.org >> https://lists.mozilla.org/listinfo/dev-platform > > _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
