Node-RED 解析 json

Question

I am trying to pull out the value "533"

{
  "d": {
    "ItemValue_1": 533
   },
   "ts": "2021-01-20T10:59:41.958591"
}

This does not work

var ItemValue_1 = msg.payload.ItemValue_1;
msg.payload = ItemValue_1;
return msg;

My result is unsuccessful

Answer 1

I was able to solve on my own, it works.

sensorMeasurement=JSON.parse(msg.payload);
msg.payload=sensorMeasurement.d;
var msgout = {payload : msg.payload.ItemValue_1}
return msgout;

Answer 2

The better way to do this is as follows:

Add a JSON node before the function node, this will turn a string payload in to a JSON object (assuming the string actually represents a JSON object).

Then if you are using a function node the following:

msg.payload = msg.payload.d.ItemValue_1;
return msg;

It is bad practice to create a new object as you did in your answer as it throws away any meta data that may be required later that is attached to the original object.

Rather than use a function node it would also be cleaner to use a change node and the Move mode to shift the msg.payload.d.ItemValue_1 to msg.payload