title: Can not parse JSON from MQTT Message in Broker
body: <p>I'm building a MQTT Server using Mosca and trying to parse MQTT Message to JSON for database store purpose. </p>
  
  <p>The code in 'published' callback below</p>
  
  <pre><code>server.on('published', (packet, client) =&gt; {
      let { payload } = packet;
      if(payload) {
          let payloadString = payload.toString();
          let payloadJson = JSON.parse(payloadString);
          console.log(payloadJson)
      }
  });
  </code></pre>
  
  <p>Sample of JSON String is: </p>
  
  <blockquote>
    <p>{"_id":"5e928105156c40000006f9e9","temperature":33,"humidity":64.9}</p>
  </blockquote>
  
  <p>But I received an error in line <code>JSON.parse</code></p>
  
  <blockquote>
    <p>SyntaxError: Unexpected token c in JSON at position 2</p>
  </blockquote>
  
  <p>How should I do to parse this message correctly ?</p>