Plans for adding new event options (capture, passive, and once)

[robwierzbowski]

Hi! Wondering if there are any plans to add new event options (capture, passive, and once). If not, I would be interested in contributing or working with developers to add them (especially once).

[triblondon]

passive is pointless to polyfill, but once would be good. Naming is interesting. This is documented under EventTarget/addEventListener:

https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener

But we already have an addEventListener polyfill, and that basic functionality is already well supported a long way back. I guess mirroring what we did with Intl, addEventListener.~options might be a good name.

[falsandtru]

Can I modify https://github.com/Financial-Times/polyfill-service/blob/master/polyfills/Event/polyfill.js to support new options?

[triblondon]

@falsandtru sure, but the trade off is we need to start serving the Event polyfill to new browsers, even though they have the majority of the functionality. So you need to either do some careful feature-testing within the polyfill, or add a separate polyfill for the new bit. Event.~options would be a possibility.

[falsandtru]

I see, I'll try to support the capture option for now.

[matthew-dean]

There's a polyfill here: https://github.com/WICG/EventListenerOptions/blob/gh-pages/EventListenerOptions.polyfill.js

However, really the only thing you're polyfilling is useCapture, since there's no way to polyfill passive event listening. Polyfilling "once" might be possible, which isn't included in the above link.

[JSteunou]

See #1386

[fvonellerts]

Has there been any progress on this topic? I usually import https://github.com/github/eventlistener-polyfill for this, the once flag can be very helpful.