mattcosta7 / headers-polyfill

A Fetch API "Headers" polyfill. Construct and operate with headers in Node.js and browser in the same way.

headers-polyfill

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-polyfill
# or
yarn add headers-polyfill

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-polyfill'

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:

• .has()
• .get()
• .set()
• .append()
• .delete()
• .forEach()

As well as the iterator methods:

• .keys()
• .values()
• .entries()

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-polyfill'

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-polyfill'

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-polyfill'

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-polyfill'


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-polyfill'

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-polyfill'

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-polyfill'

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-polyfill'

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-polyfill'

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-polyfill'

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