add check if date is valid tutorial

Author: vkarpov15

src/tutorials.js

@@ -5,6 +5,14 @@ const moment = require('moment');
 const axiosPath = require('./axiosPath');
 
 const tutorials = [
+  {
+    title: 'Check if a Date is Valid in JavaScript',
+    raw: './tutorials/fundamentals/check-if-date-is-valid.md',
+    url: '/tutorials/fundamentals/check-if-date-is-valid',
+    description: 'Got a JavaScript date that is showing up as "Invalid Date" in your console? Here\'s how you check for that.',
+    tags: ['fundamentals'],
+    date: moment('2023-08-14')
+  },
   {
     title: 'Encode base64 in JavaScript',
     raw: './tutorials/fundamentals/encode-base64.md',

tutorials/fundamentals/check-if-date-is-valid.md

@@ -0,0 +1,50 @@
+In JavaScript, a date is invalid if its `valueOf()` is [NaN](/tutorials/fundamentals/check-nan).
+
+```javascript
+const date = new Date(NaN);
+date.toString(); // 'Invalid Date'
+```
+
+This is tricky because `date` still looks like a valid date: it is still `instanceof Date`, etc.
+One way to check for an "Invalid Date" is to check if the date's `valueOf()` is `NaN`:
+
+```javascript
+Number.isNaN(date.valueOf()); // true
+
+const validDate = new Date('2022-06-01');
+Number.isNaN(validDate.valueOf()); // false
+```
+
+## Debugging Why a Date is Invalid
+
+There are two common reasons for an "Invalid Date".
+The first is passing a value that JavaScript can't interpret as a date to the `new Date()` constructor as follows.
+
+```javascript
+const badDate = new Date('foobar');
+badDate.valueOf(); // NaN
+badDate.toString(); // 'Invalid Date'
+```
+
+Invalid date strings aren't the only potential cause: passing in a numeric calculation that adds up to `NaN` also causes "Invalid Date".
+
+```javascript
+const obj = {};
+
+// 3 * obj.nonexistentProperty === undefined
+const badDate2 = new Date(3 * obj.nonexistentProperty);
+badDate2.valueOf(); // NaN
+badDate2.toString(); // 'Invalid Date'
+```
+
+A valid date can become an invalid date due to date manipulation methods like `setDate()` and `setHours()`. For example:
+
+```javascript
+const obj = {};
+
+const badDate3 = new Date('2023-06-01');
+// 3 * obj.nonexistentProperty === undefined
+badDate3.setHours(3 * obj.nonexistentProperty);
+badDate3.valueOf(); // NaN
+badDate3.toString(); // 'Invalid Date'
+```