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

Parse A Date From A Timestamp

If you are given a timestamp (seconds since the Unix epoch) and you try to parse it with JavaScript's new Date(), you are going to get a suprising result.

> 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.

> new Date(1618499080 * 1000)
Thu Apr 15 2021 10:04:40 GMT-0500 (Central Daylight Time)

Also, notice that if I run + new Date() without any argument, it provides the current timestamp in milliseconds.

> + new Date()
1618499080598