mqtt-emitter

This is a library for easily routing MQTT traffic in JavaScript. The API is the same as EventEmitter, but it automatically routes your topics behind the scenes. The parsing of topic patterns is done by mqtt-regex. This library can be used in Node, Browserify, or as a drop in JS file for the browser.

A goal of this library is to leave the actual MQTT transport up to the user so that they can use whatever MQTT connection they want for the actual transport, and just relay all incoming messages to this library for routing. Take a look at MQTT.js for node and Mows for the browser.

Example

Here's an example of how you can use the library to handle traffic from a hypothetical chat based on MQTT.

var MQTTEmitter = require("mqtt-emitter");

var events = new MQTTEmitter();

events.on("user/+name/message/#path", function(data, params) {
    var name = params.name;
    var path = params.path;
    console.log(name, "@", "/" + path.join("/"), ":", data);
});

var messages = ["hi", "what's up?", "Hey I'm new.", "How about that weather, eh?", "I know"];
var names = ["Bob", "Angelina", "xX420xNoSc0peXx"];
var count = 10;

function say_something() {
    var event = "user/" + random_from_list(names) + "/message/lobby";
    events.emit(event, random_from_list(messages));
    if (count--) setTimeout(say_something, 1000);
}

say_something();

function random_from_list(list) {
    return list[Math.floor(Math.random() * list.length)];
}

Installing & Usage

In node or browserify install with $ npm install --save mqtt-emitter

And then use it with

var MQTTEmitter = require("mqtt-emitter");
var events = new MQTTEmitter();

If you aren't using Browserify (for some crazy reason), then you can build a bundle with npm run build or npm run build-min. The bundle is UMD compatible and supports UMD, CommonJS and creates a global called MQTTEmitter if neither of those are present. Just dump the file in your HTML and you can use it with

var events = new MQTTEmitter();

API

The API is the same as EventEmitter except that on(), and emit() have custom functionality.

emitter.on(topic_pattern,callback)

topic_pattern is a MQTT topic with optional named wildcards which get parsed out. See mqtt-regex for how the patterns work.

callback takes four arguments:

• payload : The payload that was passed in with emit()
• params : The parameters parsed out using the topic pattern from the topic. See mqtt-regex for details
• topic : The topic that was emitted with emit()
• topic_pattern : The topic pattern that was used when this listener was registered

There are also hooks that you can listen for new and removed topic listeners.

// Override the default behavior with a custom callback for subscribing to topics
emitter.onadd = function (topic) {
    mqtt.subscribe(topic);
}
emitter.onremove = function (topic) {
    mqtt.unsubscribe(topic);
}

Note: Topic patterns are converted into their regular MQTT counterparts so foo/+boar/# is the same as foo/+baz/#. They both turn into foo/+/#

Note: Because of the nature of this library, the newListener and removeListener events aren't supported. Use the onadd() and onremove() hooks instead.

Note: Try to avoid topics with trailing slashes since they can lead to strange behavior.