Split string from app.getSelfPath

[SignalKuser]

hi,
i want split a string comes from

let volt = app.getSelfPath('electrical.batteries.Mo.voltage');

the payload looks like

{"meta":{"units":"V","description":"Voltage measured at or as close as possible to the device"},"value":13.2,"$source":"jbd-overkill-bms-plugin","timestamp":"2025-04-08T10:14:51.566Z"}

but i only want "value":13.2
how does it work?
thx/christian

[knolleary]

Hi @SignalKuser

When you say the payload looks like that object, do you mean the value returned by app.getSelfPath?

Assuming that is the case, and assuming its an Object and not a String, then it looks like volt.value will get you to 13.2.

However, if it is a String and not an Object, you will need to parse it to an Object first. You can do that by passing it through a JSON node, or if you want to stay inside a Function node, you can do const data = JSON.parse(volt) - then you can use data.value.

There's a section in the docs that gives some tips for working with messages - Working with messages : Node-RED
This includes how to pass messages to the debug sidebar and work out how to access individual properties.

[SignalKuser]

@knolleary

const data = JSON.parse(volt)

its an openplotter image for raspi4. inside openplotter there is Signal K. and inside Signal K there is Node Red and KIP. KIP is my UI, there is a button and when i click the button Node Red should write something in a file. electrical.batteries.Mo.voltage is a Signal K path coming from a signal k plugin and how it looks the only chance to work with this signal k path in node red is with a function like this.

msg.filename ="/home/pi/test/hello.txt";
let app = global.get('app');
let volt = app.getSelfPath('electrical.batteries.Mo.voltage');
msg.payload = volt;

return msg;

the

const data = JSON.parse(volt) 

dont work:

function : (error)
"SyntaxError: Unexpected token o in JSON at position 1"

[Colin]

Put a debug node on the output of the function node and show us what that shows.

[SignalKuser]

WOW.
yes, a debug node shows an object behind the function. now its easy to delete the other stuff. THANKS THANKS THANKS.

[SignalKuser]