add timezone-safe week of epoch scope

smhg · Nov 14, 2018 · bf528d7 · bf528d7
1 parent 49c9bd1
commit bf528d7
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diff --git a/src/util/date.js b/src/util/date.js
@@ -2,8 +2,15 @@
 
 import { dayOfYear, weekNumber } from 'weeknumber';
 
+const MINUTE = 60000;
+const WEEK = 604800000;
+
 const weekday = date => (date.getDay() + 6) % 7 + 1;
 
+const weekEpoch = new Date(1970, 0, -2); // monday before unix epoch in local timezone
+const weekOfEpoch = date =>
+  Math.abs(Math.floor((date - weekEpoch + (weekEpoch.getTimezoneOffset() - date.getTimezoneOffset()) * MINUTE) / WEEK));
+
 function modify (date, unit, value) {
   switch (unit) {
     case 'Y':
@@ -48,6 +55,7 @@ const util = {
       Y: date => date.getMonth() + 1
     },
     W: {
+      E: weekOfEpoch,
       Y: weekNumber
     },
     D: {

diff --git a/test/util.js b/test/util.js
@@ -49,6 +49,7 @@ describe('util', function () {
         assert.strictEqual(util.date.get.D.W(new Date(2014, 1, 9)), 7);
         assert.strictEqual(util.date.get.W.Y(new Date(2018, 6, 1)), 26);
         assert.strictEqual(util.date.get.W.Y(new Date(2021, 0, 1)), 53);
+        assert.strictEqual(util.date.get.W.E(new Date(1970, 0, 1)), 0);
       });
     });
   });