Cannot get length of a global array

This drives me nuts. Must be a simple error somewhere...
my function want to retrieve the length of 2 global arrays:

var se = global.get("sensors");
var sn = se.length;
var li = global.get("lights");
var ln = li.length;
var m = { payload: { "# lights": ln, "# sensors": sn }};
return (m)

However the returned values in the NR debugger are:

  # lights: undefined
  # sensors: undefined

i used the length function in other nodes, the global arrays are defined. Whats missing here?

Are you sure?

Update your function to this:

const se = global.get("sensors")
const sn = se ? se.length : 0
const li = global.get("lights")
const ln = li ? li.length : 0
    seType: typeof se,
    seIsArray: Array.isArray(se)
    liType: typeof li,
    liIsArray: Array.isArray(li)
msg.payload = { "# lights": ln, "# sensors": sn }}
return msg

and show us what you see.

Good idea!
The global variables are array of objects....
So length should return a result???

Never used the the node.warn function :wink:

Look closer at your screenshot.

its NOT an array - its a JS object.


const anArray = [{}, {}, {}]
const anObject = { "prop": "value" }

If you want the number of props (keys) in the object, then use Object.keys(se || {}).length


ah yes! a classical pitfall! thanks a lot, also for the hint with the node.warn function which seems to be perfect for debugging.


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