How to display UTC time in vega-tooltip "version": "0.5.1", - vega

Question

I use "utc" vega scale in order to display data in UTC time, but when I hover an item in the chart then tooltip show a date in local format. How to display UTC data in vega tooltip?
Here is vega tooltip config
let options = {
showAllFields: false,
fields: [
{
field: "x",
title: "Time",
formatType: "time",
format: "%x %X "+ this.props.data.Timezone
},
{
field: "y",
title: "Value",
formatType: "number"
},
{
field: "value",
title: "Time",
formatType: "time",
format: "%x %X "+this.props.data.Timezone
},
{
field: "label",
title: "Data",
formatType: "string"
},
{
field: "info",
title: "Info",
formatType: "string"
},
{
field: "startTime",
title: "Start",
formatType: "time",
format: "%x %X "+this.props.data.Timezone
},
{
field: "endTime",
title: "End",
formatType: "time",
format: "%x %X "+this.props.data.Timezone
}
]
}
vegaTooltip.vega(vegaView, options);

Answer 1

I can't judge about the data of dates you ingest, but this was discussed recently in https://github.com/altair-viz/altair/pull/1053.
The core of the matter is that you'll have to parse your datetime data in ISO-8601 standard to make your browser parse it as UTC, if you parse your data in a different format it will assumes local time zone:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/parse
Differences in assumed time zone
Given a date string of "March 7, 2014", parse() assumes a local time
zone, but given an ISO format such as "2014-03-07" it will assume a
time zone of UTC (ES5 and ECMAScript 2015). Therefore Date objects
produced using those strings may represent different moments in time
depending on the version of ECMAScript supported unless the system is
set with a local time zone of UTC. This means that two date strings
that appear equivalent may result in two different values depending on
the format of the string that is being converted.