Example JavaScript MQTT Client Using Presigned URL

// Example code of using MQTT.js to interact with AWS IoT via a presigned url.
// See https://gist.github.com/scott-stewart/2d7dc6a01d5da4326a7ad8b49d467354 for
// an exmaple of creating a presigned AWS IoT URL from a Rails controller.
// This script makes assumptions about page elements and variables not in the
// gist, but hopefully demonstrates the gist of using a presigned url approach,
// which can work to interact with AWS IoT WebSocket MQTT connections.

var iotClient = null;

function runIotClient() {
  var presignUrlRequest = new XMLHttpRequest();

  presignUrlRequest.open("GET", "/iot_presigned_url");
  presignUrlRequest.responseType = "json";
  presignUrlRequest.send();
  presignUrlRequest.onload = function() {

    iotClient = mqtt.connect(presignUrlRequest.response.url, {});

    iotClient.on("connect", function(connack) {
      iotClient.subscribe( "building/sensors/" + serialNumber + "/commands/+" )
    });

    iotClient.on("close", function () {
      if(iotClient){
        iotClient.end();
      }
      console.log('connection closed.')
    });

    iotClient.on("error", function(err) {
      console.log('Error: ' + err.toString());
    });

    iotClient.on("message", function(topic, payload) {
      if (topic === 'building/sensors/' + serialNumber + '/commands/reset') {
        var el = document.querySelector('#tempControl');
        el.value = 0
      }
    });
  }
}

function publishIt() {
  if (iotClient && iotClient.connected) {
    var topic = "building/sensors/" + serialNumber;
    var currentReading = getCurrentReading();
    var payload = JSON.stringify(currentReading);
    iotClient.publish(topic, payload);
  }
}
setInterval(publishIt, 3000);