How to get time in milliseconds since the Unix epoch in Javascript?

More ways to catch the timestamp

Variety is the spice of life. While Date.now() is a neat and tidy catch, we got other methods to sack the current timestamp, according to your JavaScript environment flavor.

For your historic ECMAScript 4 time capsule

In the era where ECMAScript 5 is still a fantasy script, express yourself with Date constructor and the cool getTime():

var milliseconds = new Date().getTime();
// "ancient" way of asking time 😄
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Another smart trick - valueOf()

Add some jazz into your developing life! Use valueOf() method, which prudently offers the identical functionality as getTime():

var milliseconds = new Date().valueOf();
// time for value! Or value of time?
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Time travel with a specific date

If you are a time traveler and wanted to convert a specific time point into the Unix timestamp in milliseconds:

var specificTime = new Date('2023-01-01T00:00:00Z').getTime();
// Hoping to see a flying car in 2023! 😃
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Specific Date object is created which represents 'January 1, 2023', and then we catch its timestamp.

Employing custom epoch converter

To embrace flexibility and swiftness utilize a function that converts input date/time into epoch time:

function toEpochMillis(input) {
  return new Date(input).getTime();
}

var epochTimeOfSpecificDate = toEpochMillis('2023-01-01T00:00:00');
// Hoping it won't be doomsday!


This reusable function not only adds flavor but also offers greater adaptability across diverse use cases.

Tackling high precision scenarios

Quadcopter may seem like a kill for "swat the fly" situation, but when the time precision is paramount, rocket launcher like performance.now() comes in handy:

var highPrecisionTime = performance.now();
// Feel like a surgeon, measuring time at its pulse!


However, remember, performance.now() launches from a different pad, not the Unix epoch. So use it for performance measurements.

Visualization

Behold the ceaseless view of time ticker tape escaping from Unix Epoch's factory:

Unix Epoch
|🕒------------------------------------> NOW

Each millisecond stitch on the infinite tape of time:

let now = Date.now(); // Grab the current millisecond count.
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Translate this as:

🕒 ==> 🕓 ==> 🕔 ==> 🕕 ==> ✨ NOW: `{now}ms`

It feels like a marathon runner tasting every footfall on the cosmic track of time.

Tricks and turns of timestamps

The passage to the current timestamp may seem a walk in the park, yet it's packed with a few surprising turns and twists:

Oh, that change in longitude!

Because the Date object works in the user's local time zone, always take a peek at the time zone conversion when handling the epoch timestamp.

Eureka, an extra second!

Unix timestamps dismiss any leap seconds. Nevertheless, if your puzzle involves aligning with the earth's decelerating rotation, remember to factor this in.

Timekeeper or a timechanger?

If your user tweaks their system clock it may pull wool over Date.now(). Avoid Houdini by using server-side timestamps or NTP synchronization for critical timekeeping tasks.