Add Parse A Date From A Timestamp as a JavaScript til

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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 - [Numbers Are Empty](javascript/numbers-are-empty.md)
 - [Object Initialization With Shorthand Property Names](javascript/object-initialization-with-shorthand-property-names.md)
 - [Obtain Undefined Value With The Void Operator](javascript/obtain-undefined-value-with-the-void-operator.md)
+- [Parse A Date From A Timestamp](javascript/parse-a-date-from-a-timestamp.md)
 - [Random Cannot Be Seeded](javascript/random-cannot-be-seeded.md)
 - [Reach Into An Object For Nested Data With Get](javascript/reach-into-an-object-for-nested-data-with-get.md)
 - [Render An Array Of Elements With React 16](javascript/render-an-array-of-elements-with-react-16.md)

javascript/parse-a-date-from-a-timestamp.md

@@ -0,0 +1,33 @@
+# Parse A Date From A Timestamp
+
+If you are given a timestamp ([seconds since the Unix
+epoch](https://stackoverflow.com/a/20823376/535590)) and you try to parse it
+with [JavaScript's `new
+Date()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/Date),
+you are going to get a suprising result.
+
+```javascript
+> new Date(1618499080)
+Mon Jan 19 1970 11:34:59 GMT-0600 (Central Standard Time)
+```
+
+1970? I was expected something more in the current millenia.
+
+This is because JavaScript's `new Date()` expects a timestamp to be in milliseconds. Passing in a seconds representation of a timestamp, when it should be milliseconds, is going to result in a time pretty near the original Unix epoch.
+
+Instead what you need to do is multiple that _seconds_ value by `1000` to get
+it in terms of milliseconds.
+
+```javascript
+> new Date(1618499080 * 1000)
+Thu Apr 15 2021 10:04:40 GMT-0500 (Central Daylight Time)
+```
+
+Also, notice that if I run [`+ new
+Date()`](https://stackoverflow.com/a/221297/535590) without any argument, it
+provides the current timestamp in milliseconds.
+
+```javascript
+> + new Date()
+1618499080598
+```