Add Easy Date Comparison With DayJS as a javascript til

javascript/easy-date-comparison-with-dayjs.md

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+# Easy Date Comparison With DayJS
+
+Let's say my application fetches dates from the server which come back in
+string form as `"YYYY-MM-DD"` and I'd like to know if those dates already
+passed. This can be done easily by wrapping dates in
+[DayJS](https://github.com/iamkun/dayjs) and using its comparison functions.
+
+```javascript
+import dayjs from 'dayjs';
+
+const today = dayjs(new Date());
+const pastDate = dayjs("2018-10-22");
+const futureDate = dayjs("2022-01-01");
+
+console.log(pastDate.isBefore(today));
+// => true
+console.log(futureDate.isBefore(today));
+// => false
+```
+
+The `dayjs()` function can be used to construct DayJS date objects from Date
+objects and strings. These can then be compared with functions like
+`isBefore()` and `isAfter()`.