4.9 Date & RegExp Objects

>>>

new Date()

Thu Apr 06 2023 13:43:30 GMT+0200 (Central European Summer Time)

The built-in Date constructor creates a new date object initialized to the current date and time. The Date.prototype.toString() method returns a string formatted according to the local timezone.

>>>

new Date(0).toUTCString()

"Thu, 01 Jan 1970 00:00:00 GMT"

The Date objects are wrappers around the number of milliseconds elapsed since Jan 01 1970 00:00:00 UTC (also known as Unix epoch).

>>>

new Date().getTime()

1680781410400

The Date.prototype.getTime() method (or Date.now() since ES5) can be used to access the current time (in milliseconds).

>>>

+(new Date(987654321000))

987654321000

It is also possible to coerce a Date object into a number to get the milliseconds elapsed.

>>>

new RegExp('[a-z]+', 'g')

/[a-z]+/g

The RegExp function is another built-in constructor that should mostly be avoided, in favor of using the shorter literal syntax.

>>>

var re = /[a-z]+/g;

>>>

re.exec('foo bar')

["foo"]

>>>

re.exec('foo bar')

["bar"]

A RegExp object instance contains both a compiled regular expression and the current matcher state (in the lastIndex property). This allows repeated calls to exec() to find repeated matches (e.g. in a loop).

>>>

re.exec('xyz')

null

This can have unintended consequences if the matching string is changed without also setting lastIndex to zero.

>>>

'foo bar baz'.match(re)

["foo", "bar", "baz"]

Use the String.prototype.match() or String.prototype.matchAll() methods instead to avoid issues.

>>>

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