Cannot read $localOffset of undefined

[jorgestg]

Describe the bug
Parsing a date with customParseFormat, then using utcOffset with keepLocaltime breaks diff

Running this snippet demonstrates the issue:

import dayjs from "https://cdn.skypack.dev/dayjs@1.10.5";
import utc from "https://cdn.skypack.dev/dayjs@1.10.5/plugin/utc";
import customParseFormat from "https://cdn.skypack.dev/dayjs@1.10.5/plugin/customParseFormat";

dayjs.extend(customParseFormat);
dayjs.extend(utc);

const dateTime = dayjs('2021-06-18', 'YYYY-MM-DD').utcOffset(-240, true); // No $x
const now = dayjs().utcOffset(-240);
const diff = dateTime.diff(now, 'days');
console.log('diff:', diff); // breaks

Uncaught TypeError: Cannot read property '$localOffset' of undefined
    at M2.u.valueOf (utc.js:63)
    at M2.m2.diff (dayjs.js:180)
    at M2.u.diff (utc.js:79)

Expected behavior
diff works as expected

I'm using this (really ugly) workaround in the meantime

;(day as any).$x = {}

Information

• Day.js Version v1.10.5
• OS: Windows
• Browser: Edge 91.0.864.48
• Time zone: UTC-04:00 PYT

[acerbisgianluca]

Hey, issue is still here. Did you find another solution?

[jorgestg]

I ended up using this:

import dayjs, { ConfigType, OpUnitType, QUnitType } from 'dayjs'
import customParseFormat from 'dayjs/plugin/customParseFormat'
import utc from 'dayjs/plugin/utc'

dayjs.extend(customParseFormat)
dayjs.extend(utc)

// Work around dayjs bug
dayjs.extend(function (_, Dayjs, __) {
  const oldDiff = Dayjs.prototype.diff
  Dayjs.prototype.diff = function (
    date: ConfigType,
    unit?: QUnitType | OpUnitType,
    float?: boolean
  ): number {
    type T = dayjs.Dayjs & { $x: {} | undefined }
    const self = this as T
    const other = date as T
    self.$x ??= {}
    other.$x ??= {}
    return oldDiff.call(self, date, unit, float)
  }
})

[acerbisgianluca]

Thx!