Fetch headers polyfill

https://developer.mozilla.org/en-US/docs/Web/API/Headers

Packed with latest and newest method from the spec: iterator, entries, keys, values, and support of for...of

const Headers = require('fetch-headers')

header = new Headers([
  ['accept', 'application/json']
  ['accept', 'text/plain']
])

Notes

This use

• WeakMap for private properties
• Symbol.iterator and Generators* for iteration
• vanilla ecmascript 6
• no transpiler
• no coffeescript or typescript

Up to date node version can just use this as is. (tested in v6.5.0)
Browsers should run this through closer-compiler, babel, Babili, browserify, webpack or equivalent.
Browsers need to include a polyfill for WeakMap and Object.keys if necessary.

Optional for those who want es5 version and don't have the time or effort to compile can use the prebuilt version

var Headers = require('fetch-headers/headers-es5.min.js')

(It has been transpiled with closure compiler)