Add an element on the go based on the value of msg.payload

[vongomben]

Hi!
Apologies in advance, this may sound a simple question.

I would like to now how to create an element of msg.payload (or better, global.payload) based on the value of msg.payload.

In other words: I am receiving a msg.payload which is a number: "1". I want to store the state "True" in global.payload.1.

I can do it by hand, but I thought it could be more elegant if it was a function, but javascript is a spice I still don't master well.

My wrong flow (super basic)
flows.json (814 Bytes)

[bakman2]

I would highly recommend to go through the documentation and how to work with messages. The videos in that document should help.

[vongomben]

Thanks.
I've seen, reviewed and looked more into the topic, and partially succeded in what I want to do.

if I send the number 3 to this function (takjen from this helpful post)

let num = msg.payload;

msg.payload = {
    Element1: num,
    Element2: "Two",
    Element3: "Three"
}
msg.payload[msg.payload.Element1] = false;

return msg;

I end up creating a msg.payload.3 set to false.

Sadly I ended up stopping in the next problem: since I want to store this values in a global object, I've previously created three global variables that I want to update.

I create them using a change node, that I inject before testing the function:

Then I edited my code in the function: I want to update one of those variables based on the number passing throught the function:

let num = msg.payload;

msg.payload = {
    Element1: num,
    Element2: "Two",
    Element3: "Three"
}
msg.payload[msg.payload.Element1] = false;

global.meridiana[msg.payload.Element1] = false;

return msg;

This gives me an error: "TypeError: Cannot set property '3' of undefined"

Why is global.meridiana["3"] undefined since I previously declared it in the change node?

---

Why I have msg.payload assigned to 3 and not payload.3 = false from this function here?

let num = msg.payload;

msg.payload[num] = false;

return msg;

Sorry for the many questions: hoping in some help

Thanks in advance.
flows (1).json (1.9 KB)

[ralphwetzel]

@vongomben

I end up creating a msg.payload.3 set to false.

There are easier ways to achieve it, but yes ... this works.
Have you tried

msg.payload[num] = false;

@vongomben

global.meridiana[msg.payload.Element1] = false;

Did you read the documentation regarding context storage? If not - I'd like to strongly recommend to do it.

@vongomben

Why I have msg.payload assigned to 3 and not payload.3 = false from this function here?

let num = msg.payload;
    console.log(typeof(msg.payload));  // check typeof msg.payload
msg.payload[num] = false;
    console.log(typeof(msg.payload));  // did you change it to another type?
return msg;

That's Javascript! I agree, it could be nicer & throw an error...