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snippets/count-week-days-between.md

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+---
+title: Count weekdays between two dates
+tags: date
+cover: organizer
+firstSeen: 2020-10-11T11:44:44+03:00
+lastUpdated: 2020-10-20T11:21:07+03:00
+---
+
+Counts the weekdays between two dates.
+
+- Use `Array.from()` to construct an array with `length` equal to the number of days between `startDate` and `endDate`.
+- Use `Array.prototype.reduce()` to iterate over the array, checking if each date is a weekday and incrementing `count`.
+- Update `startDate` with the next day each loop using `Date.prototype.getDate()` and `Date.prototype.setDate()` to advance it by one day.
+- **NOTE:** Does not take official holidays into account.
+
+```js
+const countWeekDaysBetween = (startDate, endDate) =>
+  Array
+    .from({ length: (endDate - startDate) / (1000 * 3600 * 24) })
+    .reduce(count => {
+      if (startDate.getDay() % 6 !== 0) count++;
+      startDate = new Date(startDate.setDate(startDate.getDate() + 1));
+      return count;
+    }, 0);
+```
+
+```js
+countWeekDaysBetween(new Date('Oct 05, 2020'), new Date('Oct 06, 2020')); // 1
+countWeekDaysBetween(new Date('Oct 05, 2020'), new Date('Oct 14, 2020')); // 7
+```