Accept multiple layers for Map#on

[arthurhammer]

#1002 (pull #4329) added a layer parameter to Map#on to handle mouse-related events for a specific layer. Currently, on accepts a single layer. It would be great if passing in an array of layers was supported. I believe this would make handling mouse-events even easier.

[mourner]

Thanks for creating the issue! Want to go slightly further and submit a pull request for this? Should be a quick change.

[stepankuzmin]

Hi there! If you don't mind, I've created PR for this issue #4596.

I'm not sure about comparing delegatedListener.layers with layers param in Map#off (see https://github.com/mapbox/mapbox-gl-js/pull/4596/files#diff-c6d02b0c73aa7597f4224ec35497cfe2R639). Should we preserve layers order in Map#off?

[jfirebaugh]

I'm not sure about comparing delegatedListener.layers with layers param in Map#off (see https://github.com/mapbox/mapbox-gl-js/pull/4596/files#diff-c6d02b0c73aa7597f4224ec35497cfe2R639). Should we preserve layers order in Map#off?

This is a great question. Specifically, how should the following cases behave:

• on(['a', 'b']) followed by off(['b', 'a'])
• on(['a', 'b']) followed by off(['a'])
• on(['a', 'b']) followed by on(['a']) followed by off(['a'])
• on(['a', 'b']) followed by on(['a']) followed by off(['a', 'b'])
• on(['a']) followed by on(['a', 'b']) followed by off(['a', 'b'])

The ambiguity and additional complexity of these cases makes me think we probably shouldn't implement this. If someone needs it, they can add/remove listeners in a loop.

[jfirebaugh]

Let's keep the API simple.

[stepankuzmin]

This actually makes sense. Thanks for review!