parseSpec and selection

[rickiesmooth]

I'm trying to use parseSpec and pass it an selection that's created outside of the spec, so something:

const globalSelection = vg.Selection.intersect();
const specs = {
  plot: [
    {
      mark: "areaY",
      data: {
        from: "kpis",
        filterBy: "global",
      },
      x: "date",
      y: "visits",
      stroke: "steelblue"
    },
  ],
};

vg.parseSpec(
  {
    ...specs,
    params: {
      global: { select: "intersect" },
    },
  },
  {
    options: { params: [["global", globalSelection]] },
  }
);

when I try filterBy: "$global it seems to create a new collection, and when I use filterBy: "global" the selection in the FilterGroup is "global" (so not an actual instance of the Selection class)

Is that possible, or am I using mosaic wrong? For context, I'm trying to create a date filter that would update all my clients to filter the same date range.

[mingfang]

In your spec, filterBy: "$global" is correct.
But your params may not be.
Try removing options and use just params

and const globalSelection = vg.Selection.intersect();
needs $ like const $globalSelection = vg.Selection.intersect();.

Correction: The above is not true, $ is not needed. see comment below.

Here is a working example.
https://github.com/mingfang/mosaic-svelte/blob/master/src/routes/mosaic/%2Bpage.svelte#L35

I believe this is the relevant code
https://github.com/uwdata/mosaic/blob/main/packages/vgplot/src/spec/parse-spec.js#L374

IMO
I don't agree that we should be forced to use $ for selections.
Also the $ conflicts with Svelte's use of $.

[jheer]

Thanks @mingfang. Within YAML/JSON specs the $ prefix is currently required as the parser uses that to easily identify references to params (which can even be otherwise undefined). While Svelte also use $, Mosaic's requirement here only applies to these external YAML/JSON files. You are not required to use a $ prefix if writing JavaScript code directly.

[mingfang]

@jheer I was able to confirm that $ is not needed in Javascript code. Thanks.

[rickiesmooth]

thanks for the example @mingfang, that's very succinct and exactly what I'm trying to do! Also good to know that the $ is not necessary @jheer, thank you