Messenger

Messenger is a Req/Rep Pub/Sub library for iframes and workers.

Features

Allows messages to be exchanged between ...

• the main window and one or more iframes / workers.
• multiple iframes.
• multiple components.

Installation

via npm:

npm i @knowledgecode/messenger

Usage

import { MessengerClient, MessengerServer } from '@knowledgecode/messenger';

ES Modules:

<script type="module">
  import { MessengerClient, MessengerServer } from '/path/to/esm/messenger.js';
</script>

Traditional:

<script src="/path/to/umd/messenger.js"></script>
<script>
  // It is provided with the global variable name "messenger".
  const { MessengerClient, MessengerServer } = self.messenger;
</script>

Simple Example

main.js

import { MessengerClient } from '/path/to/esm/messenger.js';

const messenger = new MessengerClient();
const worker = new Worker('/path/to/worker.js');

(async () => {
    await messenger.connect('example', worker);

    const answer = await messenger.req('add', { x: 2, y: 3 });

    console.log(answer);    // => 5

    messenger.send('close');
    messenger.disconnect();
})();

worker.js

importScripts('/path/to/umd/messenger.js');

const { MessengerServer } = self.messenger;
const messenger = new MessengerServer('example', self);

messenger.bind('add', data => {
    return data.x + data.y;
});

messenger.bind('close', () => {
    messenger.close();
    // Close this worker.
    self.close();
});

MessengerClient API

constructor()

const messenger = new MessengerClient();

connect(name, [endpoint[, options]])

• {string} name - unique name of the MessengerServer to connect to
• {Object} [endpoint] - an object that actually executes the postMessage()
• {Object} [options] - connection options

The MessengerClient must connect to a MessengerServer via endpoint before communication can begin. To identify the MessengerServer to connect to, pass the unique name of the MessengerServer as the first argument. The endpoint is the object that actually executes the postMessage(). If omitted, it is assumed that self is set. The options are connection options and members of this object are targetOrigin and timeout (msec). If the timeout is omitted, this method will wait forever for a successful connection.

// To connect from the main window to a iframe.
const iframe = window.frames[0];

await messenger.connect('iframe', iframe, { targetOrigin: '*', timeout: 1000 })
    .catch(e => console.log(e));

// To connect from the main window to a worker.
const worker = new Worker('/path/to/worker.js');

await messenger.connect('worker', worker, { timeout: 1000 })
    .catch(e => console.log(e));

disconnect()

Disconnects from the server.

messenger.disconnect();

send(topic[, data])

• {string} topic - topic name
• {Object} [data] - an object to send

Sends a message (some object) to a topic. This method does not wait for any reply. A MessengerServer can receive the message if it is bound to the same topic name in advance.

messenger.send('greeting', { hello: 'world' });

req(topic[, data[, timeout]])

• {string} topic - topic name
• {Object} [data] - an object to send
• {number} [timeout] - timeout (msec)

Sends a message (some object) to a topic. This method waits for some reply unlike send(). If timeout (msec) is omitted, this method waits forever for some reply.

const answer = await messenger.req('add', { x: 2, y: 3 })

console.log(answer);

await messenger.req('add', { x: 2, y: 3 }, 5000)
    .catch(e => console.log(e));    // Catch timeout error.

subscribe(topic, listener)

• {string} topic - topic name
• {Function} listener - a listener to receive published messages

Subscribes to messages on a topic.

messenger.subscribe('news', data => console.log(data));

unsubscribe(topic[, listener])

Unsubscribes to messages on a topic. If listener is omitted, all listeners for the topic are cleared.

• {string} topic - topic name
• {Function} [listener] - a listener to receive published messages

const listener = data => console.log(data);
messenger.subscribe('news', listener);

messenger.unsubscribe('news', listener);

MessengerServer API

constructor(name, [endpoint])

• {string} name - unique name of the MessengerServer
• {Object} [endpoint] - an object that actually executes the postMessage()

const messenger = new MessengerServer('server', self);

The name is a unique name by which clients identify this MessengerServer. The endpoint is the object that actually executes the postMessage(). If omitted, it is assumed that self is set.

bind(topic, listener)

• {string} topic - topic name
• {Function} listener - a listener to receive messages

Binds a listener to listen for messages on a topic. The topic names must be unique, no other listener than the first can bind on the same topic name. This method returns true or false as binding result.

messenger.bind('greeting', data => console.log(data));

messenger.bind('add', data => {
    // Reply to client.
    return data.x + data.y;
});

publish(topic, data)

• {string} topic - topic name
• {Object} data - an object to publish

Publish a message (some object) to all subscribers on a topic. This method does not wait for reply from the subscribers, and also does not fail even there are no subscribers at all.

messenger.publish('notification', 'The process completed successfully.');

close()

Closes all connections and shuts down the server.

messenger.close();

Browser support

Chrome, Safari, Firefox, Edge

License

MIT