embark/site/source/docs/messages_javascript.md

title: Messages in JavaScript layout: docs

Embark's companion library EmbarkJS comes with some convenient APIs to easily subscribe to and sending messages using messages protocols like Whisper. In this guide we'll take a closer look how this works.

Make sure to read our guide in using EmbarkJS first.

Setting up EmbarkJS

By default Embark will initialize EmbarkJS with the provider configured at config/communication.js. However if we are using EmbarkJS directly or wish to change the provider configuration at runtime, we can do so using the setProvider() method:

EmbarkJS.Messages.setProvider('whisper')

Listening to messages

We can subscribe to channels using the listenTo() method by specifying a list of channel topics like this:

EmbarkJS.Messages.listenTo({
  topic: ['topic1', 'topic2']
}).then(message {
  console.log('received: ' + message);
});

Sending messages

Sending messages can be done using the sendMessage() method and it's entirely up to use whether we want to send plain text messages or even objects.

Here's how to send a plain text message to the sometopic topic:

EmbarkJS.Messages.sendMessage({
  topic: 'sometopic',
  data: 'hello world'
});

And this code snippet shows how to send an object structure:

EmbarkJS.Messages.sendMessage({
  topic: 'sometopic',
  data: { msg: 'hello world' }
});

{% notification info 'On topic arrays:' %} Array of topics are considered an AND. In Whisper you can use another array for OR combinations of several topics e.g ["topic1", ["topic2", "topic3"]] => topic1 AND (topic2 OR topic 3). {% endnotification %}