<HTML>
<HEAD>
    <TITLE> Wizzer.cn </TITLE>
    <meta charset="utf-8">
</HEAD>

<BODY>
<script src="https://cdnjs.cloudflare.com/ajax/libs/paho-mqtt/1.0.1/mqttws31.min.js" type="text/javascript"></script>
F12打开控制台
<br>
<br>
<input type="button" value="0. start and subscribe topic /topic_back " onclick="doStart()">
<br>
<br>
<input type="button" value="1. send message to topic /topic/mqttwk " onclick="sendMessage()">
<script>
    var hostname = '127.0.0.1',
        port = 9995,
        clientId = 