Question 1

What is a Unix timestamp?

Accepted Answer

A Unix timestamp (also called Epoch time or POSIX time) is the number of seconds that have elapsed since 1 January 1970 00:00:00 UTC. It is a simple, timezone-independent way to represent a point in time as a single integer.

Question 2

How do I tell if a timestamp is in seconds or milliseconds?

Accepted Answer

Timestamps in seconds are typically 10 digits long (e.g. 1700000000), while millisecond timestamps are 13 digits (e.g. 1700000000000). JavaScript's Date.now() returns milliseconds, whereas most Unix command-line tools return seconds.

Question 3

What is the Year 2038 problem?

Accepted Answer

Many older systems store Unix timestamps as a signed 32-bit integer, which can hold a maximum value of 2,147,483,647. That value corresponds to 19 January 2038 03:14:07 UTC, after which the counter overflows. Modern 64-bit systems and JavaScript are unaffected because they use larger number types.

Question 4

How do I get the current Unix timestamp in JavaScript?

Accepted Answer

Use Date.now() to get the current time in milliseconds, or Math.floor(Date.now() / 1000) for seconds. You can also use new Date().getTime() which is equivalent to Date.now().