[BUG]: hoveranywhere / clickanywhere return incorrect timestamps for date axes with local time zones

[Domino987]

Description

The new hoveranywhere and clickanywhere functionality introduced in PR #7707 appears to return timestamps in ms since 1970 for the UTC (or axis-internal time) instead of the actual hovered/clicked data coordinate in local time.

In the example, when hovering or clicking at the very beginning of a date axis range that starts at local midnight, the returned timestamp is shifted by the local timezone offset.

Reproduction

JSFiddle: https://jsfiddle.net/mky0s84a/1/

Using the following setup:

const startOfDay = new Date();
startOfDay.setHours(0, 0, 0, 0);

const now = new Date();

const layout_time = {
  xaxis: {
    type: 'date',
    range: [startOfDay, now]
  },
  hoveranywhere: true,
  clickanywhere: true
};

gd.on('plotly_hover', function(data) {
  console.log(new Date(data.xvals[0]).toISOString());
});

gd.on('plotly_click', function(data) {
  console.log(new Date(data.xvals[0]).toISOString());
});

Steps to Reproduce

1. Open the JSFiddle.
2. Hover or click at the extreme left side of the plot area.
3. Inspect the logged value from data.xvals[0].

Expected Behavior

The returned value should correspond to the actual x-coordinate under the cursor.

For a user in UTC+2, hovering/clicking at local midnight on 2026-05-31 should return:

2026-05-30T22:00:00.000Z

because that is the UTC representation of local midnight.

Actual Behavior

The returned value is:

2026-05-31T00:00:00.000Z

which corresponds to midnight UTC rather than the hovered local-time position on the axis.

Notes

• The axis range is initialized using JavaScript Date objects in local time.
• The issue is reproducible for both hoveranywhere and clickanywhere.
• Existing point hover behavior appears to correctly account for timezone conversion, while the anywhere-events seem to return a different timestamp basis.
• It looks like the coordinate returned by data.xvals[0] may be using an internal UTC axis value instead of the user-visible axis coordinate.

Environment

• Plotly.js version containing PR Enable Hover and Click Events Anywhere #7707
• Browser: (fill in)
• OS: (fill in)
• Timezone tested: UTC+2 (Europe/Berlin)

[godfengliang]

I've opened PR #7818 to fix this. The issue is that ax.p2c() on date axes returns a display-time value (local-time components encoded as UTC ms) rather than true UTC milliseconds. The fix applies a timezone correction after the p2c call in the hover handler to convert back to true UTC ms, matching what trace data points return.

[camdecoster]

Thanks for the bug report! We'll be talking about this as a team soon and will follow up.

[robertclaus]

@emilykl is following up on some nuances this touches on related to timezones this week.