CODEWITHSUNDEEP
javascriptarraysobject
Richard
Richard

Reputation: 261

JavaScript Objects, Arrays, confusion?

My JavaScript MQTT Client (Paho) is subscribed to a Topic on a MQTT Broker (Mosquitto). I use JSON.parse to convert the array to an object.

client.onMessageArrived = onMessageArrived;
var myObj = JSON.parse(message.payloadString);

The payload looks like this,

{"applicationID":"4","applicationName":"Sensor-Module-241","deviceName":"P-241","devEUI":"00face0173800241","rxInfo":[{"mac":"0004a30b0022813c","rssi":-22,"loRaSNR":10.2,"name":"PiXCL-G000","latitude":45.485524299999994,"longitude":-75.6969496,"altitude":54}],"txInfo":{"frequency":903000000,"dataRate":{"modulation":"LORA","bandwidth":500,"spreadFactor":8},"adr":true,"codeRate":"4/5"},"fCnt":10101,"fPort":99,"data":"AGhQAXMq+AJnAHgDAAEEAAEFAQEGAQEHAgEYCAIB0A==","object":{"digitalInput":{"3":1,"4":1},"digitalOutput":{"5":1,"6":1},"analogInput":{"7":2.8,"8":4.64},"temperatureSensor":{"2":12},"humiditySensor":{"0":40},"barometer":{"1":1100}}}

Using typeof I get,

 console.log('payLoadString: ', typeof 'payLoadString');//string
    console.log('message.payloadString: ', typeof message.payloadString);//string
    console.log('myObj: ', typeof myObj);//object
    console.log('myObj.applicationID: ', typeof myObj.applicationID);//string
    console.log('myObj.applicationName: ', typeof myObj.applicationName);//string
    console.log('myObj.deviceName: ', typeof myObj.deviceName);//string
    console.log('myObj.devEUI: ', typeof myObj.devEUI);//string
    console.log('myObj.rxInfo: ', typeof myObj.rxInfo);//object
    console.log('myObj.txInfo: ', typeof myObj.txInfo);//object
    console.log('myObj.fCnt: ', typeof myObj.fCnt);//number
    console.log('myObj.fPort: ', typeof myObj.fPort);//number
    console.log('myObj.data: ', typeof myObj.data);//string
    console.log('myObj.object: ', typeof myObj.object);//object

If I do the following,

I get stuff I do not understand,

console.log('Object.entries(myObj): ', Object.entries(myObj));
   var n = Object.entries(myObj);
   console.log('typeof: n: ', n);
   console.log('typeof: Object.entries(myObj): ', typeof Object.entries(myObj));

Object.entries(myObj):  
Array [ […], […], […], […], […], […], […], […], […], […] ]
utility.js:114:2
typeof: n:  
Array [ […], […], […], […], […], […], […], […], […], […] ]
utility.js:116:2
typeof: Object.entries(myObj):  object

I thought in the beginning that I had used JSON.parse to make the object, but now I don't know what it is. Then, I wanted to get the information (name:values) contained in rxInfo and also in the ??? that is named object (note: this entry follows the one with the name data) and I want to get the individual name:values from this as well, along with their name:values.

In summary, I want to get the name:value pairs from what I had thought was a json message from the mqtt broker, such that I can use the names in a column in a table and the corresponding values in the adjacent column of the table in a browser.

I keep trying but end up with various things that seem so weird. For instance, this Object.entries(myObj.rxInfo[0]) gives me

Array [ […], […], […], […], […], […], […] ]

and I can get the length, and use Object.entries(), Object.keys() and Object.values() on this, but when I try to access a specific entry using a string key, console.log(Object.entries(myObj.rxInfo[0].rssi)), I end up with

Array []

and when I do this,

console.log(Object.entries(myObj.rxInfo[0]).rssi);

I end up with

undefined

ARRGGGHHHH! I must admit I am not very knowledgeable about JavaScript, but had thought that this would not be very hard, and it's turning out to be quite confusing.

Upvotes: 1

Views: 281

Answers (1)

Stephen
Stephen

Reputation: 3727

Calling typeof on an array will return object which leads to confusion, in the example you provided rxInfo is an array. You can try myObj.rxInfo[0].rssi and you should see the value you expected.

You can check if the object is an actual array using isArray or testing the prototype Object.prototype.toString.call(data) == '[object Array]';

Upvotes: 2

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