Splitting a Message Payload in Node-Red

This tutorial is part of a series of project tutorials I will be creating for beginners looking to get familiar with node-red by creating actual flows.

In this simple project we will look at splitting a simple message payload, and then display the data in a text box and on gauges on a dashboard.

The payload consists of a simple string containing temperature and humidity readings separated by a ampersand (&).

{“topic”:”node1/temperatureandmoisture”,”payload”:”26.81&1024″,”qos”:0,”retain”:false,”_msgid”:”2b22bffa.9eff4″}

To split it we use the split method to split the string into an array.

The array will look like this [26.8,1024].

Next there are two main approaches to dealing with the data:

• Place data in an Object
• Assign data directly to message properties

Placing data in an Object

We place the data into a JavaScript object and assign to the payload before returning. The code is shown below.

var data=msg.payload;
var temp=data.split("&");
var out={};
out["temperature"]=temp[0];
out["humidity"]=temp[1];
msg.payload=out;
return msg;

The output would look like this.

{temperature:26.8,humidity:1024}

To display in a text box we change the value format form msg.payload to msg.payload.humidity as shown below.

To display on a gauge we need to insert change nodes to change as shown below:

Assign data directly to message properties

The second approach is simpler and we use a message property for humidity and temperature and now our code  looks like this :

var data=msg.payload;
var temp=data.split("&");
msg.temperature=temp[0];
msg.humidity=temp[1];
return msg;

To display it in a text box set the value format to msg.humidity instead of msg.payload.

However if you want to display it on a gauge then the value must be in the msg.payload field.

To do this we can use change nodes set as follows:

Both Approaches use the same nodes but they are configured differently. The flow look like this:

The dashboard like this:

The flows for both approaches are available to download below:

Related Tutorials and Resources

• Understanding and Using The Node-Red Message Object
• Filtering MQTT Topics (commands and Responses) in Node-Red
• Republishing HTTP Data Over MQTT with Node-Red
• MQTT Data Logger -Node-Red