Format Date - Support ISO Week Year (GGGG)

Co-Authored-By: Dylan Lathrum <19830705+dylancyclone@users.noreply.github.com>
Co-Authored-By: Joseph Hale, MS SE <47901316+thehale@users.noreply.github.com>

docs/src/pages/quasar-utils/date-utils.md

@@ -67,6 +67,7 @@ Available format tokens:
 | Day of Week | <ul><li>**d**: 0 1 ... 5 6</li><li>**dd**: Su Mo ... Fr Sa</li><li>**ddd**: Sun Mon ... Fri Sat</li><li>**dddd**: Sunday Monday ... Friday Saturday</li></ul> |
 | Day of Week (ISO) | <ul><li>**E**: 1 2 ... 6 7</li></ul> |
 | Week of Year | <ul><li>**w**: 1 2 ... 52 53</li><li>**ww**: 01 02 ... 52 53</li></ul> |
+| ISO Week Year | <ul><li>**GG**: 70 71 ... 29 30</li><li>**GGGG**: 1970 1971 ... 2029 2030</li></ul> |
 | Hour | <ul><li>**H**: 0 1 ... 22 23</li><li>**HH**: 00 01 ... 22 23</li><li>**h**: 0 ... 11 12</li><li>**hh**: 01 02 ... 11 12</li></ul> |
 | Minute | <ul><li>**m**: 0 1 ... 58 59</li><li>**mm**: 00 01 ... 58 59</li></ul> |
 | Second | <ul><li>**s**: 0 1 ... 58 59</li><li>**ss**: 00 01 ... 58 59</li></ul> |
@@ -307,6 +308,16 @@ const newDate = new Date(2017, 0, 4)
 const week = date.getWeekOfYear(newDate) // `week` is 1
 ```
 
+To get the [ISO week year](https://en.wikipedia.org/wiki/ISO_week_date) for a given date object use:
+
+```js
+import { date } from 'quasar'
+
+const newDate = new Date(2022, 0, 1) // End of the last week of 2021
+const year = date.getISOWeekYear(newDate) // `year` is 2021
+const week = date.getWeekOfYear(newDate) // `week` is 52
+```
+
 To get the day number in year for a given date object use:
 
 ```js

ui/src/utils/date.js

@@ -497,6 +497,16 @@ export function getWeekOfYear (date) {
   return 1 + Math.floor(weekDiff)
 }
 
+export function getISOWeekYear (date) {
+  // Remove time components of date
+  const thursday = new Date(date.getFullYear(), date.getMonth(), date.getDate())
+
+  // Change date to Thursday same week
+  thursday.setDate(thursday.getDate() - ((thursday.getDay() + 6) % 7) + 3)
+
+  return thursday.getFullYear() 
+}
+
 function getDayIdentifier (date) {
   return date.getFullYear() * 10000 + date.getMonth() * 100 + date.getDate()
 }
@@ -750,6 +760,22 @@ const formatter = {
       : date.getFullYear()
   },
 
+  GG (date, dateLocale, forcedYear) {
+    // workaround for < 1900 with new Date()
+    const g = this.GGGG(date, dateLocale, forcedYear) % 100
+    return g >= 0
+      ? pad(g)
+      : '-' + pad(Math.abs(g))
+  },
+
+  // Year: 1900, 1901, ..., 2099
+  GGGG (date, _dateLocale, forcedYear) {
+    // workaround for < 1900 with new Date()
+    return forcedYear !== void 0 && forcedYear !== null
+      ? forcedYear
+      : getISOWeekYear(date)
+  },
+
   // Month: 1, 2, ..., 12
   M (date) {
     return date.getMonth() + 1
@@ -985,6 +1011,7 @@ export default {
   buildDate,
   getDayOfWeek,
   getWeekOfYear,
+  getISOWeekYear,
   isBetweenDates,
   addToDate,
   subtractFromDate,