headers-polyfill

A native "Headers" class polyfill.

Usage no npm install needed!

<script type="module">
  import headersPolyfill from 'https://cdn.skypack.dev/headers-polyfill';
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README

Published version Build status

headers-utils

A Headers class polyfill and transformation library.

Motivation

Various request issuing libraries utilize a different format of headers. This library chooses the Headers instance as the middle-ground between server and client, and provides functions to convert that instance to primitives and vice-versa.

Install

$ npm install headers-utils

Polyfill

This package exports the Headers class that polyfills the native window.Headers implementation. This allows you to construct and manage headers using the same API in non-browser environments.

import { Headers } from 'headers-utils'

const headers = new Headers({
  Accept: '*/*',
  'Content-Type': 'application/json',
})

headers.get('accept') // "*/*"

Methods

The Headers polyfill instance supports the same methods as the standard Headers instance:

As well as the iterator methods:

Custom methods

In addition, the polyfill instance has the following methods:

  • .all()

Returns the object of the normalized header name/value pairs.

const headers = new Headers({
  Accept: '*/*',
  'Content-Type': 'application/json',
})

headers.all()
// { "accept": "*/*", "content-type": "application/json" }
  • .raw()

Similar to the .all() method, .raw() returns an object consisting of the header name/value pairs, but preserving raw header names.

const headers = new Headers({
  Accept: '*/*',
  'Content-Type': 'application/json',
})

headers.raw()
// { "Accept": "*/*", "Content-Type": "application/json" }

Transformations

Headers ⭢ N

  • headersToString: (h: Headers): string
import { headersToString } from 'headers-utils'

headersToString(
  new Headers({
    connection: 'keep-alive',
    'content-type': ['text/plain', 'image/png'],
  })
)
// connetion: keep-alive
// content-type: text/plain, image/png
  • headersToList: (h: Headers): Array<[string, string | string[]]>
import { headersToList } from 'headers-utils'

headersToList(
  new Headers({
    connection: 'keep-alive',
    'content-type': ['text/plain', 'image/png'],
  })
)
// [['connection', 'keep-alive'], ['content-type', ['text/plain', 'image/png']]]
  • headersToObject: (h: Headers): Record<string, string | string[]>
import { headersToObject } from 'headers-utils'

headersToObject(
  new Headers({
    connection: 'keep-alive',
    'content-type': ['text/plain', 'image/png'],
  })
)
// { connection: 'keep-alive', 'content-type': ['text/plain', 'image/png'] }

N ⭢ Headers

  • stringToHeaders: (s: string): Headers
import { stringToHeaders } from 'headers-utils'


const stringToHeaders(`
connection: keep-alive
content-type: text/plain, image/png
`)
// Headers { connection: 'keep-alive', 'content-type': ['text/plain', 'image/png'] }
  • listToHeaders: (l: Array<[string, string | string[]]>): Headers
import { listToHeaders } from 'headers-utils'

listToHeaders([
  ['connection', 'keep-alive'],
  ['content-type', ['text/plain', 'image/png']],
])
// Headers { connection: 'keep-alive', 'content-type': ['text/plain', 'image/png'] }
  • objectToHeaders: (o: Record<string, string | string[] | undefined>): Headers
import { objectToHeaders } from 'headers-utils'

objectToHeaders({
  connection: 'keep-alive',
  'content-type': ['text/plain', 'image/png'],
})
// Headers { connection: 'keep-alive', 'content-type': ['text/plain', 'image/png'] }

Utilities

  • reduceHeadersObject: <R>(o: Record<string, string | string[]>, reducer: (acc: R, name: string, value: string | string[]) => R) => R
import { reduceHeadersObject } from 'headers-utils'

reduceHeadersObject <
  HeadersObject >
  ({
    Accept: '*/*',
    'Content-Type': ['application/json', 'text/plain'],
  },
  (headers, name, value) => {
    headers[name.toLowerCase()] = value
    return headers
  },
  {})
// { 'accept': '*/*', 'content-type': ['application/json', 'text/plain'] }
  • appendHeader: (o: Record<string, string | string[]>, n: string, v: string | string[]): Record<string, string | string[]>
import { appendHeader } from 'headers-utils'

appendHeader(
  { 'content-type': 'application/json' },
  'content-type',
  'text/plain'
)
// { 'content-type': ['application/json', 'text/plain']}
  • flattenHeadersList: (l: Array<[string, string | string[]]>): Array<string, string>
import { flattenHeadersList } from 'headers-utils'

flattenHeadersList([['content-type', ['text/plain', 'image/png']]])
// ['content-type', 'text/plain; image/png']
  • flattenHeadersObject: (o: Record<string, string | string[]>): Record<string, string>
import { flattenHeadersObject } from 'headers-utils'

flattenHeadersObject({
  'content-type': ['text/plain', 'image/png'],
})
// { 'content-type': 'text/plain; image/png' }