Indexing into flow/global scope array element using variable

[Eric]

I have a flow scoped array that I initialized like this:

flow.set('status',[true,true,true,true,true,true,true,true,true,true]);

Later on, I'm doing some processing to figure out which element of that array I want to make a change to. So I can do this if I want to change element [5] of that array.

flow.set('status[5]', msg.payload);

That works fine. But I actually want to use a variable instead of hard coding in the index value, so more like this:

flow.set('status[index_match]', msg.payload);

But node-red throws an error when I use a variable "index_match".

function : (error)"Error: Invalid property expression: unexpected i at position 7"

I can can kinda see why, a variable inside the single quotes is weird. Is there some other syntax for addressing an element of a flow scoped array? I'd rather not have to resort to this ugliness:

if (index_match == 0)
  flow.set('status[0]', msg.payload);
else if (index_match == 1)
 flow.set('status[1]', msg.payload);
else if (index_match == 2)
 flow.set('status[2]', msg.payload);

Edit: I also tried this syntax with the index outside the quotes.

flow.set('status'[index_match], msg.payload);

This runs, but doesn't actually change the array element, so doesn't do what I'm intending.

[kuema]

The key of the context functions is actually an expression evaluated by the runtime, it's behaves not like a map or dictionary. That is the reason why something like flow.set('status[5]', msg.payload); works in the first place.

Now if you do flow.set('status[index_match]', msg.payload);, the runtime evaluates status[index_match], but your local index_match variable is unknown to it. So it throws an error.

I see two possible solutions:

Get the status array from context and use it in your script like a normal array

let status = flow.get('status');
status[index_match] = msg.payload;

That will work because your array (or any object) is accessed by reference.

OR

use a template string or string concatenation and build the string beforehand.

flow.set(`status[${index_match}]`, msg.payload);