Multi-axis zoom and original zoom limits

[joshkel]

This fixes #522 and #523. I put it together for my own use, so everything's in one branch, but I'm happy to submit as smaller PRs for discussion and review whenever someone's ready to take a look at it.

Thank you.

[kurkle]

Had a quick look, looks good. The .gitignore changes should be split off, if those are needed at all. Not a fan of passing the state around that much (actually just the number of args), but I think its better than getting the state everywhere.

[kurkle]

Something is broken:

[test-karma] ✗ /base/test/fixtures/zoom/zoom-reset.js
[test-karma] RangeError: invalid digits value: NaN thrown

[joshkel]

Thanks. I fixed the test failure.

I wasn't a big fan of the number of parameters, either, but I didn't see a clean way of reducing it.

I noticed that the module exports zoomFunctions and panFunctions, so that third-party custom scale classes can register specialized handling for zoom and pan (#169). This PR would change the function signature of those functions, which would be a SemVer breaking change. Should I move the chartState parameter to the end of each of the zoomFunctions and panFunctions to avoid this? Or, since the issue is still open and the feature is not yet documented, is it okay to make changes?

[kurkle]

Good catch the breaking change on zoomFunctions and panFunctions.

Maybe the extra parameters should be avoided at least on those functions, as the getState should be fast enough to just call again in there.

[joshkel]

Thanks for the feedback.

If I avoid the extra parameter for zoomFunctions and panFunctions and instead retrieve the state within the updateRange function that they call, then most of the changes that I'd originally made end up being unnecessary.

So it's probably still a bit cleaner to call getState once within the top-level public API methods, and use it in places like this, and pass it to storeOriginalScaleLimits, but it's no longer needed for this PR. Would you like me to go ahead and do it?

[kurkle]

I'd be ok having it done in this pr, if you are willing to do it ;)

[joshkel]

@kurkle Done. Thanks.