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Summary

The issue is not with the JSON, but it's with the use of the expression interpreter. It looks like using a string date is not working with the expression interpreter.

Live Example

See https://codepen.io/kmcgrady/pen/YzjKQXy for an example

Observations

The docs seem confusing and suggest to not allow string dates.

However, vega-lite takes the input and just passes it on.

This definitely causes a problem because the interpreter takes it and fails.

So the problem can be one of the following:

1. Vega Lite does not validate the datetime to be proper numerical values
2. The interpreter is not open to accepting a string date or numerical values

I think the answer is (2) The interpreter should accept both. I think String dates are common and would match what already works. I can create a PR if there's an example.

Versions

vega-embed@6.21.0
vega@5.22.1
vega-lite@5.6.0
vega-interpreter@1.0.4

JSON Example

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "Google's stock price over time.",
  "data": {"url": "https://cdn.jsdelivr.net/npm/vega-datasets@2.5.3/data/stocks.csv"},
  "transform": [{"filter": "datum.symbol==='GOOG'"}],
  "mark": "line",
  "encoding": {
    "x": {
      "field": "date",
      "scale": {"domain": ["2004-08-01T00:00:00", "2010-03-01T00:00:00"]},
      "type": "temporal"
    },
    "y": {"field": "price", "type": "quantitative"}
  }
}