Undefined global variables

[Peter Scargill]

And for today's daft question...

I want to know if a global variable exists... and I'm getting no-where.

if (global.get("fredsik")!==null) msg.payload=1; else msg.payload=0;

return msg;

I get 1 no matter what variable name I put in there... can someone put me out of my misery? What am I doing wrong?

Pete.

[Giles Roadnight]

you're doing a strict comparison with null so if it is undefined it will still be 1.

try 

global.get("variableName")!=null

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[Peter Scargill]

You are in fact correct – thank you – mind you – node-red does gripe with a little triangle telling you not to do this. Would be nice to understand this more clearly.

 

Pete.

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[Nicholas O'Leary]

JavaScript likes to make this sort of comparison non-obvious.

If you want to use a strict comparison (because using a non-strict comparison against null is discouraged), you should compare against undefined as that is what a non-existant value will return.

if (global.get("fredsik")===undefined) msg.payload=1; else msg.payload=0;

However, if you do global.set('fredisk',null) at any point, then the above comparison won't work any more, because it does have a value, it just happens to have a value of null.

Nick

[Giles Roadnight]

you could of course do if (global.get("fredsik")!==null && global.get("fredisk")!==undefined)

[Peter Scargill]

Thank you guys for today’s enlightenment. Excellent.