PAHO mqtt client(mqttws31.js) and JSON.parse() does not work

Question

I am publishing simple JSON string {"TMP":"-15.5826"} to the web client. Message appears in message.payloadString I can print it to in html but I could not parse the message with JSON.parse(). obj and data is undefined..this is the main problem, to solve this I used JSON.stringify() first, this time message parsed but data is still undefined. It seems stringify adds extra double quotes and invalidates json string. mqttws31.js is the latest, broker is mosquitto 1.4.4. What should I do to get JSON.parse() working?

publishing is through mosquitto command:mosquitto_pub -t /main/SENSOR -m {"TMP":"-15.5826"}

function onMessageArrived(message) {

    var topic = message.destinationName;
    var payload = message.payloadString;

    $('#ws').prepend('<li class=messagelist>' + topic + ' = ' + payload + '</li>');

    var jsonString = JSON.stringify(payload);

    obj = JSON.parse(jsonString); //parse with extra double quotes
    //obj = JSON.parse(payload);  //does not parse

    var data = obj.TMP;
    alert(data);
};

What's the result of this: `console.log(typeof payload, payload)`? Stringifying and subsequently parsing doesn't make sense. — robertklep, Jan 17 '16 at 07:39
quotes missing. so i published {\"TMP\":"15.5826"}.. now it works..thank you very much. — thesubscriber, Jan 17 '16 at 09:01

score 0 · Accepted Answer · answered Jan 17 '16 at 08:57

You need to prevent your shell from removing the double quotes during publishing, by using single quotes around the JSON string:

mosquitto_pub -t /main/SENSOR -m '{"TMP":"-15.5826"}'

When that's done, you can use JSON.parse(payload) (no need for JSON.stringify()).

PAHO mqtt client(mqttws31.js) and JSON.parse() does not work

1 Answers1