It uses postMessage to send cross-domain events, which is used to provide mock HTTP APIs (fetch, WebSocket, XMLHTTPRequest etc.). Simplified version

How do I use it

Theres three components to this module: the Server, Adapter and Client.

Server

Simply serve a HTML file on a domain from which you want to make requests from (HTTP domain for example), with the following (use a bundler like Webpack, Parcel etc):

import { Server } from 'cors-bypass'

const server = new Server()

Without a bundler

<body>
  <script src="./node_modules/cors-bypass/lib/server.bundle.js"></script>
</body>

Adapter

Next you need a HTML file from the domain that will make requests (your web app's domain). The adapter is in control of forwarding requests from a client located on any page of your site, to the server (using a BroadcastChannel).

import { Adapter } from 'cors-bypass'
const adapter = new Adapter()

Without a bundler

<body>
  <script src="./node_modules/cors-bypass/lib/adapter.bundle.js"></script>
</body>

Client

As long as the Adapter is running in a different tab (on the same domain as the client), you will be able to make requests.

// Located somewhere on https://your-site.com
import * as BypassCors from 'cors-bypass'

const client = new BypassCors.Client()

await client.getServer() // null - no server connected yet
await client.openServerInNewTab({
  serverUrl: 'http://random-domain.com/server.html',
  adapterUrl: 'https://your-site.com/adapter.html'
})
await client.getServer() // { id: 123, url: 'http://random-domain.com/server.html' }

// Create a WebSocket (websocket is loaded in the server tab, but it's API is available on this page)
const ws = new BypassCors.WebSocket('ws://echo.websocket.org')
ws.onopen = () => ws.send('hello')
ws.onmessage = ({ data }) => console.log('received', data)

Use cases

HTTP requests for Offline PWAs

As using a Service Worker require HTTPS, it's impossible to connect to local devices which only support HTTP.

Using this module does requires the user to open an extra window, but it lets you bypass cors.

FAQs

What is cors-bypass?

Is cors-bypass popular?

Is cors-bypass well maintained?

Last updated on 07 Jan 2019

Did you know?

Socket for GitHub automatically highlights issues in each pull request and monitors the health of all your open source dependencies. Discover the contents of your packages and block harmful activity before you install or update your dependencies.

Install