WranggleRpc transport using window.postMessage for windows and iframes

Usage no npm install needed!

<script type="module">
  import wranggleRpcPostMessageTransport from 'https://cdn.skypack.dev/@wranggle/rpc-post-message-transport';



A WranggleRpc transport for browser windows (including iframes and web/service workers), sending and receiving messages with message events.


If you are using the full @wranggle/rpc package, the PostMessageTransport is already bundled within. You can import/require it with:

import { WranggleRpc, PostMessageTransport } from '@wranggle/rpc';
// or
const { WranggleRpc, PostMessageTransport } = require('@wranggle/rpc');

Unbundled Alternative

If you prefer using just the packages you need, the unbundled es6 is also available on NPM:

yarn add @wranggle/rpc-core @wranggle/rpc-post-message-transport
# or
npm install @wranggle/rpc-core @wranggle/rpc-post-message-transport 

Unbundled import:

import WranggleRpc from '@wranggle/rpc-core';
import PostMessageTransport from '@wranggle/rpc-post-message-transport';


When creating your WranggleRpc endpoint, you can use the postMessage shortcut to also construct this transport. Eg:

const rpc = new WranggleRpc({
  postmessage: opts,
  channel: 'some-channel'

Or create a new instance yourself:

const rpc = new WranggleRpc({
  transport: new PostMessageTransport(opts),
  channel: 'some-channel'


Send/receive windows

To be able to use postMessage, you need to specify which window to use for sending and for listening.

Note: if using an iframe, remember to pass in its contentWindow (eg, myIframe.contentWindow) not the iframe DOM element.

  • sendingWindow a reference to the window for sending messages. It is the window in: window.postMessage().

  • receivingWindow a reference to the window that listens for messages. The window in: window.addEventListener('message', listener)

  • targetWindow a shortcut that sets both sendingWindow and receivingWindow options to the same window. (Using the current window/global is common.)


  • sendToOrigin The targetOrigin value used when calling targetWindow.postMessage. Set it the origin / base url of the receiving window. (Eg, https://example.edu) If this option is not set, it will use the current origin (meaning both communicating windows must be on the same origin.)

  • shouldReceive Filter that determines if a received message should be used or ignored. It a function is passed, it is passed the event.origin string of the received message, accepting the message only if the function returns true. If a string is passed, it will expect the message origin to match it exactly. (Eg, https://example.edu) If this option is not set, the transport will only accept messages originating from the same origin.


parent window and iframe on the same origin:

Endpoint for parent window:

const iframe = document.querySelector('#my-iframe');
const rpc = new WranggleRpc({
  channel: 'our-same-origin-frames-channel',
  postMessage: {
    targetWindow: iframe.contentWindow,

Endpoint inside iframe:

const rpc = new WranggleRpc({
  channel: 'our-same-origin-frames-channel',
  postMessage: {
    targetWindow: window,