JavaScript dates

The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap seconds (in ISO 8601: 1970-01-01T00:00:00Z). Literally speaking the epoch is Unix time 0 (midnight 1/1/1970), but ‘epoch’ is often used as a synonym for Unix time.

Human-readable time	Seconds	Milliseconds
1 second	1	1000 ms
1 minute	60 s	60,000 ms
1 hour	3,600 s	3,600,000 ms
1 day	86,400 s	86,400,000 ms
1 week	604,800 s	604,800,000 ms
1 month	2,629,746 s	2,629,746,000 ms
1 year	31,556,952 s	31,556,952,000 ms

Get the current epoch time

The getTime() method returns the time in milliseconds.

Math.floor(new Date().getTime() / 1000.0) // 1676457318

Convert from epoch to human-readable date

const date = new Date(1676457318 * 1000) // Wed Feb 15 2023 10:35:18 GMT+0000 (Greenwich Mean Time)

Date methods

date.toDateString() // 'Wed Feb 15 2023'
date.toJSON() // '2023-02-15T10:35:18.000Z'
date.toUTCString() // 'Wed, 15 Feb 2023 10:35:18 GMT'
date.toLocaleString() // '2/15/2023, 10:35:18 AM'
date.toLocaleTimeString() // '10:35:18 AM'
date.getDate() // 15
date.getTime() // 1676457318000
date.getUTCDay() // 3
date.getMinutes() // 35
date.getHours() // 10
date.getMonth() // 1 - months are zero-indexed
date.getFullYear() // 2023

Formatting with Intl.DateTimeFormat

For more control over date formatting without external libraries:

const date = new Date()

// Basic formatting
new Intl.DateTimeFormat('en-GB').format(date) // '15/02/2023'
new Intl.DateTimeFormat('en-US').format(date) // '2/15/2023'

// With options
new Intl.DateTimeFormat('en-US', {
  weekday: 'long',
  year: 'numeric',
  month: 'long',
  day: 'numeric',
}).format(date) // 'Wednesday, February 15, 2023'

// Relative time
const rtf = new Intl.RelativeTimeFormat('en', { numeric: 'auto' })
rtf.format(-1, 'day') // 'yesterday'
rtf.format(2, 'hour') // 'in 2 hours'

Date.now() shorthand

Date.now() // 1676457318000 (current timestamp in ms)

ISO string parsing

new Date('2023-02-15T10:35:18.000Z') // Parses ISO 8601 format