Add Easy Date Comparison With DayJS as a javascript til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_718 TILs and counting..._
+_719 TILs and counting..._
 
 ---
 
@@ -247,6 +247,7 @@ _718 TILs and counting..._
 - [Default And Named Exports From The Same Module](javascript/default-and-named-exports-from-the-same-module.md)
 - [Destructuring The Rest Of An Array](javascript/destructuring-the-rest-of-an-array.md)
 - [Enable ES7 Transforms With react-rails](javascript/enable-es7-transforms-with-react-rails.md)
+- [Easy Date Comparison With DayJS](javascript/easy-date-comparison-with-dayjs.md)
 - [Expand Emojis With The Spread Operator](javascript/expand-emojis-with-the-spread-operator.md)
 - [Fill An Input With A Ton Of Text](javascript/fill-an-input-with-a-ton-of-text.md)
 - [Freeze An Object, Sorta](javascript/freeze-an-object-sorta.md)

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

@@ -0,0 +1,23 @@
+# 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()`.