Incorrect decoding of local dates in Safari.

[Fil]

instead of treating new Date("2018-04-25T11:00") as a local date, Safari parses it as a UTC date and returns it with the tz difference added. This fix detects the situation by checking TWO local dates (one in winter, one in summer) which should return hour 0, and if one of them is not 0 it's the Safari bug. In that case, and if the date string that is passed is local (no "Z"), we shift it accordingly.

I don't know how to write a node test for this, but the following notebook shows the fix on Safari: https://observablehq.com/d/7e8b78e5050258ae

Fixes https://github.com/d3/d3-dsv/issues/45

[mbostock]

Some suggestions:

• Compute tzFix once on startup rather than every time autoType is invoked.

• Store the local timezone offset string (e.g., -07:00) rather than a boolean, or null if the workaround is not needed.

• Add the local timezone offset string to the input value if m[7] is falsey, prior to parsing the date, rather than parsing the input and then offsetting by milliseconds.

if (fixtz && !m[7]) value += fixtz;
value = new Date(value)

[mbostock]

Oh, and most importantly: don’t add the local timezone offset if the specified input value doesn’t contain a time (T…, m[4] should be truthy, I believe).

if (fixtz && !!m[4] && !m[7]) value += fixtz;
value = new Date(value)

In other words, this should always be parsed as UTC (and should already work as-is in all browsers):

new Date("2018-04-25")

And this would give an invalid date:

new Date("2018-04-25-07:00")

Let’s make sure we have a test for that.

[Fil]

I've implemented the suggested changes, but I realize the fix is wrong in winter for summer dates, and vice versa. (Because the offset depends on the daylight savings time at the date we read.) So, more work needed…

[mbostock]

Okay, well here’s potentially a simpler hack to force Safari to parse local dates. Change the format:

new Date("2019/09/02 11:00")

Something like value.replace(/-/g, "/").replace(/T/, " ") should work.

[Fil]

Much simpler! I've updated the test notebook. I still have no idea how to test for it in node (can we monkey patch the Date class?).