Normalize which using keyCode and charCode

[syranide]

Is there a good reason why this isn't being done already? key and char are mentioned in the code, but char has since been deprecated in the standard and key relies on the browser to implement, leaving which as the only cross-browser solution for now. There doesn't seem to be a full-featured polyfill either that could be recommended as a substitute for key-support.

IE8 and older browsers don't support which, but only keyCode and charCode, seeing as we have the synthetic events, normalizing behavior according to (old) standards should be better than pushing it onto the developer.

I propose that this PR be closed and that this solution be used instead #607

[petehunt]

can you do:

if (typeof event.which !== 'undefined') {
  return event.which;
} else if (typeof event.charCode !== 'undefined') {
  return event.charCode;
}

return event.keyCode;

[sophiebits]

You can just do event.which != null, which is a bit shorter than the typeof check (and is what jQuery does, fwiw). Also I think that code would be clearer if the third branch were in an else.

[syranide]

@petehunt Certainly, and I don't disagree stylistically, but I did copy the style from https://github.com/facebook/react/blob/master/src/event/synthetic/SyntheticWheelEvent.js and https://github.com/facebook/react/blob/master/src/event/synthetic/SyntheticMouseEvent.js

Still want me to change? (It would be a quick fix to change the others)

I tinkered a bit with key and only non-character keys are possible to implement consistently and cross-browser. Even IE11 and FF that are the only to currently implement key-support at this time are broken implementations (although non-character key support is working in both, so that's that). Perhaps there's some merit to actually identifying non-character keys and always supplying them as key as fallback, as that is by far the most common use I would say.

I whipped up a simple implementation and it ends up at ~650B before uglify and gzip, sounds interesting?