feat: Added method to retrieve week of the year

Author: naulacambra

src/index.js

@@ -120,6 +120,14 @@ class Dayjs {
     return this.$M
   }
 
+  week() {
+    const day = this.$W || 7 // Return sunday as 7
+    // Create date at nearest thursday
+    const ins = new Date(this.$y, this.$M, (this.$D - day) + 4)
+    const yearStart = new Date(Date.UTC(this.$y, 0, 1)) // Get first day of year
+    return Math.ceil((((ins - yearStart) / 86400000) + 1) / 7) // Calculate weeks
+  }
+
   day() {
     return this.$W
   }

test/get-set.test.js

@@ -18,6 +18,10 @@ it('Month', () => {
   expect(dayjs().month()).toBe(moment().month())
 })
 
+it('Week', () => {
+  expect(dayjs().week()).toBe(moment().week())
+})
+
 it('Day of Week', () => {
   expect(dayjs().day()).toBe(moment().day())
 })

test/index.d.test.ts

@@ -16,6 +16,8 @@ dayjs().year()
 
 dayjs().month()
 
+dayjs().week()
+
 dayjs().date()
 
 dayjs().day()