MQTT主要使用在物联网中，是一种双工通信，属于ws协议长连接
that.client =new Paho.MQTT.Client(
ip, Number(port),"/ws",ID);
//ip:服务器IP；
port:服务器端口；
'/ws':固定就是ws协议；
ID:自己随便编一个字符串；
that.client.connect({useSSL:false,onSuccess:onConnect});
useSSL:是否保密；
onSuccess:链接成功后执行的回调函数；
function onConnect() {
console.log("onConnected");
//订阅的主题
let id = localStorage.getItem("cncId");
console.log(id);
var topic ="/cnc/" + id +"/servo_loading";
console.log(topic);
//订阅主题
that.client.subscribe(topic);
console.log("subscribed");
}
that.client.onConnectionLost =onConnectionLost;
//注册连接断开处理事件
that.client.onMessageArrived =onMessageArrived;
//注册消息接收处理事件
function onConnectionLost(responseObject) {
if (responseObject.errorCode !==0) {
console.log("onConnectionLost:"+responseObject.errorMessage);
console.log("连接已断开");
}
};
function onMessageArrived(message) {
//console.log("收到消息:"+message.payloadString);
//console.log("主题："+message.destinationName);
//that.msg = JSON.parse(message.payloadString);
that.msg = JSON.parse(message);
console.log(that.msg);
}
