customParseFormat strict mode bug

Describe the bug Using the format string “YYYY-MM-DD HH:mm:ss ZZ”, parsing certain strings returns Invalid Date when it should return a date:

var format = "YYYY-MM-DD HH:mm:ss ZZ";
var ok = dayjs("2018-03-01 00:01:00 +0000", format, true);
var bad = dayjs("2018-04-01 00:01:00 +0000", format, true);

where bad is:

{
  "$D": 1
  "$H": 1
  "$L": "en"
  "$M": 3
  "$W": 0
  "$d": Invalid Date
  "$m": 1
  "$ms": 0
  "$s": 0
  "$u": undefined
  "$y": 2018
}

The parsing is successful if strict mode is not used. The problem seems to be in the customParseFormat.js line:

      if (isStrict && date !== this.format(format)) {

where the date that the plugin has parsed is not matching the default output from dayjs.format(). In the above case:

"2018-04-01 00:01:00 +0000" !== "2018-04-01 01:01:00 +0100"

but the same bug will effect parsing any date where the timezone doesn’t match whatever local timezone/dst dayjs uses. eg. “2018-03-01 00:01:00 +0600”, “2018-04-01 00:01:00 -0200”, etc.

Expected behavior bad should be a valid date object.

Information

• Day.js Version: v1.8.28
• OS: Windows 7
• Browser: Firefox 77, Chrome 83
• Time zone: UTC+00:00 DST (British Summer Time)

[iamkun]

Bug confirmed. Strict mode does not work good with parsing timezone (ZZ)

I’m looking for a way to solve it.

[ivansieder]

@iamkun is there anything else we can do to help get this pull request merged?