feat: add vega interpreter as dependency and support custom interpreter

[domoritz]

Needs vega/vega#2712

[domoritz]

Alternatively, I could try to load the expression parser from vega (unless otherwise specified) and expect users who bundle their app to always provide the expression parser directly.

However, it looks like the parser is pretty small and it is nice that we don't require users to do any extra work to use the expression parser.

[domoritz]

Someone should redo this pull request.

[domoritz]

Will redo if anyone requests this feature.

[stefanw]

Hey @domoritz, I would appreciate this feature. Right now, passing ast: true does not help much without a custom vega build because vega.expressionInterpreter needs to exist which it does not when using ES module bundling. I'm currently working around it like this to make sure expr on the vega view is set:

import * as vega from 'vega';
import { expressionInterpreter } from 'vega-interpreter';
import embed from 'vega-embed';

class CSPVegaView extends vega.View {
  constructor (runtime, opt) {
    opt.expr = expressionInterpreter
    super(runtime, opt);
  }
}

// ... define el, spec
embed(el, spec, {
    viewClass: CSPVegaView,
    ast: true
  })

It's a bit cumbersome. I think either shipping vega-embed with vega-interpreter as a dependency or allowing to pass in your own expr option to embed could be a solution.

---

Also: congratulations on your recent career step! Awesome that you still find the time to work on vega stuff.

[domoritz]

Oh hello. Nice to see you here. I'll put it back in my queue to finish this up.

[domoritz]

I put it in my heap instead.