The UNIX timestamp is an integer that represents the number of seconds elapsed since January 1 1970.

On UNIX-like machines, which include Linux and macOS, you can type date +%s in the terminal and get the UNIX timestamp back:

$ date +%s
1524379940

The current timestamp can be fetched by calling the now() method on the Date object:

Date.now()

You could get the same value by calling

new Date().getTime()

or

new Date().valueOf()

Note: IE8 and below do not have the now() method on Date. Look for a polyfill if you need to support IE8 and below, or use new Date().getTime() if Date.now is undefined (as that’s what a polyfill would do)

The timestamp in JavaScript is expressed in milliseconds.

To get the timestamp expressed in seconds, convert it using:

Math.floor(Date.now() / 1000)

Note: some tutorials use Math.round(), but that will approximate to the next second even if the second is not fully completed.

or, less readable:

~~(Date.now() / 1000)

I’ve seen tutorials using

+new Date

which might seem a weird statement, but it’s perfectly correct JavaScript code. The unary operator + automatically calls the valueOf() method on any object it is assigned to, which returns the timestamp (in milliseconds). The problem with this code is that you instantiate a new Date object that’s immediately discarded.

To generate a date from a timestamp, use new Date(<timestamp>) but make sure you pass a number (a string will get you an “invalid date” result - use parseInt() in doubt)