headers

headers is a toolkit for working with HTTP headers in JavaScript.

HTTP headers contain a wealth of information:

Who is sending this request?
What's in the payload and how is it encoded?
What is the filename of this file upload?
and much more!

The built-in JavaScript Headers interface accepts and gives you strings for everything, which you're probably used to parsing and stringifying manually as needed. This library aims to give you a more fluent interface for all of this information. Similar to how the DOM gives you programmatic access to HTML documents, headers gives you access to HTTP headers.

Installation

npm install @mjackson/headers

Overview

import Headers from '@mjackson/headers';

let headers = new Headers();

// Accept
headers.accept = { 'text/html': 1, 'text/*': 0.9 };
// or headers.accept = 'text/html,text/*;q=0.9';

headers.accept.mediaTypes; // [ 'text/html', 'text/*' ]
Object.fromEntries(headers.accept.entries()); // { 'text/html': 1, 'text/*': 0.9 }

headers.accept.accepts('text/html'); // true
headers.accept.accepts('text/plain'); // true
headers.accept.accepts('image/jpeg'); // false

headers.accept.getPreferred(['text/plain', 'text/html']); // 'text/html'

headers.accept.set('text/plain', 0.9);
headers.accept.set('text/*', 0.8);

headers.get('Accept'); // 'text/html,text/plain;q=0.9,text/*;q=0.8'

// Accept-Encoding
headers.acceptEncoding = { gzip: 1, deflate: 0.8 };
// or headers.acceptEncoding = 'gzip, deflate;q=0.8';

headers.acceptEncoding.accepts('gzip'); // true
headers.acceptEncoding.accepts('br'); // false

headers.acceptEncoding.getPreferred(['gzip', 'deflate']); // 'gzip'

// Accept-Language
headers.acceptLanguage = { 'en-US': 1, en: 0.9 };
// or headers.acceptLanguage = 'en-US,en;q=0.9';

headers.acceptLanguage.languages; // [ 'en-us', 'en' ]
Object.fromEntries(headers.acceptLanguage.entries()); // { 'en-us': 1, en: 0.9 }

headers.acceptLanguage.accepts('en'); // true
headers.acceptLanguage.accepts('ja'); // false

headers.acceptLanguage.getPreferred(['en-US', 'en-GB']); // 'en-US'
headers.acceptLanguage.getPreferred(['en', 'fr']); // 'en'

// Accept-Ranges
headers.acceptRanges = 'bytes';

// Connection
headers.connection = 'close';

// Content-Type
headers.contentType = 'application/json; charset=utf-8';

headers.contentType.mediaType; // "application/json"
headers.contentType.charset; // "utf-8"

headers.contentType.charset = 'iso-8859-1';

headers.get('Content-Type'); // "application/json; charset=iso-8859-1"

// Content-Disposition
headers.contentDisposition =
  'attachment; filename="example.pdf"; filename*=UTF-8\'\'%E4%BE%8B%E5%AD%90.pdf';

headers.contentDisposition.type; // 'attachment'
headers.contentDisposition.filename; // 'example.pdf'
headers.contentDisposition.filenameSplat; // 'UTF-8\'\'%E4%BE%8B%E5%AD%90.pdf'
headers.contentDisposition.preferredFilename; // '例子.pdf'

// Cookie
headers.cookie = 'session_id=abc123; user_id=12345';

headers.cookie.get('session_id'); // 'abc123'
headers.cookie.get('user_id'); // '12345'

headers.cookie.set('theme', 'dark');
headers.get('Cookie'); // 'session_id=abc123; user_id=12345; theme=dark'

// Host
headers.host = 'example.com';

// Last-Modified
headers.lastModified = new Date();
// or headers.lastModified = new Date().getTime();
headers.get('Last-Modified'); // 'Fri, 20 Dec 2024 08:08:05 GMT'

// Location
headers.location = 'https://example.com';

// Referer
headers.referer = 'https://example.com/';

// Set-Cookie
headers.setCookie = ['session_id=abc123; Path=/; HttpOnly'];

headers.setCookie[0].name; // 'session_id'
headers.setCookie[0].value; // 'abc123'
headers.setCookie[0].path; // '/'
headers.setCookie[0].httpOnly; // true

// Modifying Set-Cookie attributes
headers.setCookie[0].maxAge = 3600;
headers.setCookie[0].secure = true;

headers.get('Set-Cookie'); // 'session_id=abc123; Path=/; HttpOnly; Max-Age=3600; Secure'

// Setting multiple cookies is easy, it's just an array
headers.setCookie.push('user_id=12345; Path=/api; Secure');
// or headers.setCookie = [...headers.setCookie, '...']

// Accessing multiple Set-Cookie headers
for (let cookie of headers.getSetCookie()) {
  console.log(cookie);
}
// session_id=abc123; Path=/; HttpOnly; Max-Age=3600; Secure
// user_id=12345; Path=/api; Secure

Headers can be initialized with an object config:

let headers = new Headers({
  contentType: {
    mediaType: 'text/html',
    charset: 'utf-8',
  },
  setCookie: [
    { name: 'session', value: 'abc', path: '/' },
    { name: 'theme', value: 'dark', expires: new Date('2021-12-31T23:59:59Z') },
  ],
});

console.log(`${headers}`);
// Content-Type: text/html; charset=utf-8
// Set-Cookie: session=abc; Path=/
// Set-Cookie: theme=dark; Expires=Fri, 31 Dec 2021 23:59:59 GMT

Headers works just like DOM's Headers (it's a subclass) so you can use them anywhere you need a Headers.

import Headers from '@mjackson/headers';

// Use in a fetch()
let response = await fetch('https://example.com', {
  headers: new Headers(),
});

// Convert from DOM Headers
let headers = new Headers(response.headers);

headers.set('Content-Type', 'text/html');
headers.get('Content-Type'); // "text/html"

If you're familiar with using DOM Headers, everything works as you'd expect.

Headers are iterable:

let headers = new Headers({
  'Content-Type': 'application/json',
  'X-API-Key': 'secret-key',
  'Accept-Language': 'en-US,en;q=0.9',
});

for (let [name, value] of headers) {
  console.log(`${name}: ${value}`);
}
// Content-Type: application/json
// X-Api-Key: secret-key
// Accept-Language: en-US,en;q=0.9

If you're assembling HTTP messages, you can easily convert to a multiline string suitable for using as a Request/Response header block:

let headers = new Headers({
  'Content-Type': 'application/json',
  'Accept-Language': 'en-US,en;q=0.9',
});

console.log(`${headers}`);
// Content-Type: text/html
// Accept-Language: en-US,en;q=0.9

Low-level API

In addition to the high-level Headers API, headers also provides a rich set of primitives you can use to work with just about any complex HTTP header value. Each header class includes a spec-compliant parser (the constructor), stringifier (toString), and getters/setters for all relevant attributes. Classes for headers that contain a list of fields, like Cookie, are Iterable.

All individual header classes may be initialized with either a) the string value of the header or b) an init object specific to that header.

The following headers are currently supported:

headers

If you need support for a header that isn't listed here, please send a PR! The goal is to have first-class support for all common HTTP headers.

Accept

let header = new Accept('text/html;text/*;q=0.9');

header.has('text/html'); // true
header.has('text/plain'); // false

header.accepts('text/html'); // true
header.accepts('text/plain'); // true
header.accepts('text/*'); // true
header.accepts('image/jpeg'); // false

header.getPreferred(['text/html', 'text/plain']); // 'text/html'

for (let [mediaType, quality] of header) {
  // ...
}

// Alternative init styles
let header = new Accept({ 'text/html': 1, 'text/*': 0.9 });
let header = new Accept(['text/html', ['text/*', 0.9]]);

Accept-Encoding

let header = new AcceptEncoding('gzip,deflate;q=0.9');

header.has('gzip'); // true
header.has('br'); // false

header.accepts('gzip'); // true
header.accepts('deflate'); // true
header.accepts('identity'); // true
header.accepts('br'); // true

header.getPreferred(['gzip', 'deflate']); // 'gzip'

for (let [encoding, weight] of header) {
  // ...
}

// Alternative init styles
let header = new AcceptEncoding({ gzip: 1, deflate: 0.9 });
let header = new AcceptEncoding(['gzip', ['deflate', 0.9]]);

Accept-Language

let header = new AcceptLanguage('en-US,en;q=0.9');

header.has('en-US'); // true
header.has('en-GB'); // false

header.accepts('en-US'); // true
header.accepts('en-GB'); // true
header.accepts('en'); // true
header.accepts('fr'); // true

header.getPreferred(['en-US', 'en-GB']); // 'en-US'
header.getPreferred(['en', 'fr']); // 'en'

for (let [language, quality] of header) {
  // ...
}

// Alternative init styles
let header = new AcceptLanguage({ 'en-US': 1, en: 0.9 });
let header = new AcceptLanguage(['en-US', ['en', 0.9]]);

Cache-Control

import { CacheControl } from '@mjackson/headers';

let header = new CacheControl('public, max-age=3600, s-maxage=3600');
header.public; // true
header.maxAge; // 3600
header.sMaxage; // 3600

// Alternative init style
let header = new CacheControl({ public: true, maxAge: 3600 });

Content-Disposition

import { ContentDisposition } from '@mjackson/headers';

let header = new ContentDisposition('attachment; name=file1; filename=file1.txt');
header.type; // "attachment"
header.name; // "file1"
header.filename; // "file1.txt"
header.preferredFilename; // "file1.txt"

// Alternative init style
let header = new ContentDisposition({
  type: 'attachment',
  name: 'file1',
  filename: 'file1.txt',
});

Content-Type

import { ContentType } from '@mjackson/headers';

let header = new ContentType('text/html; charset=utf-8');
header.mediaType; // "text/html"
header.boundary; // undefined
header.charset; // "utf-8"

// Alternative init style
let header = new ContentType({
  mediaType: 'multipart/form-data',
  boundary: '------WebKitFormBoundary12345',
  charset: 'utf-8',
});

import { Cookie } from '@mjackson/headers';

let header = new Cookie('theme=dark; session_id=123');
header.get('theme'); // "dark"
header.set('theme', 'light');
header.delete('theme');
header.has('session_id'); // true

// Iterate over cookie name/value pairs
for (let [name, value] of header) {
  // ...
}

// Alternative init styles
let header = new Cookie({ theme: 'dark', session_id: '123' });
let header = new Cookie([
  ['theme', 'dark'],
  ['session_id', '123'],
]);

import { SetCookie } from '@mjackson/headers';

let header = new SetCookie('session_id=abc; Domain=example.com; Path=/; Secure; HttpOnly');
header.name; // "session_id"
header.value; // "abc"
header.domain; // "example.com"
header.path; // "/"
header.secure; // true
header.httpOnly; // true
header.sameSite; // undefined
header.maxAge; // undefined
header.expires; // undefined

// Alternative init styles
let header = new SetCookie({
  name: 'session_id',
  value: 'abc',
  domain: 'example.com',
  path: '/',
  secure: true,
  httpOnly: true,
});

License

See LICENSE