Add class to colorbar; extract out class names

[monfera]

See the separate commits.

[etpinard]

Can I ask why? Looks good though.

[monfera]

@etpinard crossfilter mostly operates via the regular API, eg. Plotly.addTracesfor adding a salient trace that shows the selected points (will likely switch to the persistent selection for this), but not always. For example, adding a salient trace will duplicate the colorbar, but the original one shouldn't be shown. It is possible to Plotly.restyle the original trace to make the colorbar go away, and another Plotly.restyle to make it come back. These calls are expensive and the dashboard is quite slow as it is. To meet functional needs at decent speed, there are some shortcuts, mostly, setting the opacity of something to zero and back. These calls are infinitely fast, just one selection.style.

While this relies on implementation detail - the scenegraph - , it's unexposed and internal to the crossfilter code ie. we can trivially remove these once there is a fast, single-call API (such as Plotly.react as you suggest) that can take care of all changes with no duplicated overhead.

In the process, I saw a missing classname and thought it's good practice to add a class name anyway (and extract out the class names). As a matter of convention I automatically add class names to scenegraph elements because not doing so might introduce shallow, avoidable gotchas during dev, and makes the code more fragile, eg. when changing the code. Relying on SVG tags eg. circle is not as good because, in the future, we may always replace a terminal node with a g and there goes some selection that might have relied on tags.

[etpinard]

💃