parsehttpdate

Parses the value of the Date header in HTTP responses.

Description

Parses date-times from HTTP headers such as Date, Last-Modified, and Expires. An example of such a date-time is:

Tue, 15 Nov 1994 08:12:31 GMT

The format is defined by HTTP/1.1 (and HTTP/1.0) and is a subset of the specification used by the Internet Message Format.

Installation

Install parsehttpdate using npm or Yarn and import the function:

import parseHttpDate from 'parseHttpDate';

Alternatively, include parsehttpdate through unpkg:

<script src="https://unpkg.com/parsehttpdate@^1.0.7"></script>

This alternative makes the function available at window.parseHttpDate.

Usage

parseHttpDate('Wed, 21 Oct 2015 07:28:00 GMT');

Combined with fetch

This is how you can determine the time according to your server:

fetch('/')
.then(({ headers }) => {
	if (headers.has('Date')) {
		return headers.get('Date');
	} else /* if (false == headers.has('Date')) */ {
		throw new Error('The response lacks a Date header');
	}
})
.then(parseHttpDate)
.then(date => {
	console.log(date.toTimeString());
});

This is the same example using an async function:

async function getServerDate() {
	const { headers } = await fetch('/');
	if (headers.has('Date')) {
		return parseHttpDate(headers.get('Date'));
	} else /* if (false == headers.has('Date')) */ {
		throw new Error('The response lacks a Date header');
	}
}

getServerDate()
.then(date => {
	console.log(date.toTimeString());
});

Advanced usage

If you are fairly certain the input is formatted correctly, you can squeeze out some extra performance by turning off validation.

parseHttpDate('Wed, 21 Oct 2015 07:28:00 GMT', false);

Other formats

Does your date-time look nothing like the example above, but rather something like this?

1994-11-06T08:49:37Z

Congratulations: your date-time is formatted according to ISO 8601. You don't need this library. You don't need any library:

new Date('1994-11-06T08:49:37Z');

The HTTP/1.1 specification defines two obsolete formats besides the preferred format of the examples above:

Sunday, 06-Nov-94 08:49:37 GMT

Sun Nov 6 08:49:37 1994

This library does not support those; the supported format has been the preferred one since 1996. Please create an issue if your use case requires the others.

License (X11/MIT)

Copyright (c) 2018-2021 Pimm "de Chinchilla" Hogeling

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

The Software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and noninfringement. in no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the Software or the use or other dealings in the Software.