feat: 🎸 Support utcOffset as a string (HH:mm | HHmm)

Provide support string support to utcOffset method. Valid string values
formats for utcOffset method are +HH:mm, -HH:mm, +HHmm and -HHmm.

✅ Closes: iamkun#1085

src/constant.js

@@ -28,3 +28,5 @@ export const INVALID_DATE_STRING = 'Invalid Date'
 // regex
 export const REGEX_PARSE = /^(\d{4})[-/]?(\d{1,2})?[-/]?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?[.:]?(\d+)?$/
 export const REGEX_FORMAT = /\[([^\]]+)]|Y{1,4}|M{1,4}|D{1,2}|d{1,4}|H{1,2}|h{1,2}|a|A|m{1,2}|s{1,2}|Z{1,2}|SSS/g
+export const REGEX_VALID_OFFSET_FORMAT = /[+-]\d\d(?::?\d\d)?/g
+export const REGEX_OFFSET_HOURS_MINUTES_FORMAT = /([+-]|\d\d)/g

src/plugin/utc/index.js

@@ -1,4 +1,23 @@
-import { MILLISECONDS_A_MINUTE, MIN } from '../../constant'
+import { MILLISECONDS_A_MINUTE, MIN, REGEX_VALID_OFFSET_FORMAT, REGEX_OFFSET_HOURS_MINUTES_FORMAT } from '../../constant'
+
+
+function offsetFromString(value = '') {
+  const offset = value.match(REGEX_VALID_OFFSET_FORMAT)
+
+  if (!offset) {
+    return null
+  }
+
+  const [indicator, hoursOffset, minutesOffset] = `${offset[0]}`.match(REGEX_OFFSET_HOURS_MINUTES_FORMAT) || ['-', 0, 0]
+  const totalOffsetInMinutes = (+hoursOffset * 60) + (+minutesOffset)
+
+  if (totalOffsetInMinutes === 0) {
+    return 0
+  }
+
+  return indicator === '+' ? totalOffsetInMinutes : -totalOffsetInMinutes
+}
+
 
 export default (option, Dayjs, dayjs) => {
   const proto = Dayjs.prototype
@@ -59,6 +78,12 @@ export default (option, Dayjs, dayjs) => {
       }
       return oldUtcOffset.call(this)
     }
+    if (typeof input === 'string') {
+      input = offsetFromString(input)
+      if (input === null) {
+        return this
+      }
+    }
     const offset = Math.abs(input) <= 16 ? input * 60 : input
     let ins = this
     if (keepLocalTime) {