Node-RED解析Payload数据遇阻，寻求简易解决方案

Hey there! I see you've got your Node-RED setup talking to multiple PLCs, but ran into a snag parsing that payload. The good news is you don't need splice or split here—those are for working with strings, and your payload is already a JavaScript object (Node-RED automatically parses JSON payloads by default).

Here's the simplest way to extract the d field (or any other field) using a Function node:

Step 1: Basic Extraction (Payload is Already an Object) #

Drop a Function node into your flow, and paste this code:

// Extract the "d" value from the payload object
const dValue = msg.payload.d;

// Replace original payload with just the "d" value for downstream nodes
msg.payload = dValue;
// OR keep the original payload and add the d value as a separate property:
// msg.deviceReading = dValue;

return msg;

If you want to pull out multiple fields at once, you can use object destructuring for cleaner code:

// Grab all fields you need in one line
const { d, dt, ts, q } = msg.payload;

// Example: Build a custom payload with renamed fields
msg.payload = {
  deviceReading: d,
  deviceType: dt,
  timestamp: ts,
  quality: q
};

return msg;

Why Your splice/split Approach Didn't Work #

split() and splice() are methods for strings and arrays, respectively. Since your payload is already parsed into a JS object, you can directly access its properties using dot notation (msg.payload.d) or bracket notation (msg.payload["d"])—no need to manipulate raw strings here.

Edge Case: If Your Payload is a String (Not Parsed) #

If for some reason Node-RED didn't auto-parse the JSON into an object (unlikely, but possible), you can first convert it to an object with JSON.parse():

// Convert string payload to a usable object first
const payloadObj = JSON.parse(msg.payload);
const dValue = payloadObj.d;

msg.payload = dValue;
return msg;

That's it—this should get you up and running in no time!

内容的提问来源于stack exchange，提问作者Kevin Williams