CODEWITHSUNDEEP
node.js
John Smith
John Smith

Reputation: 4353

Node - look up the value of an arbitrary variable

Take this code for an example:

(() => {
    const data = []
    const ws = new WebSocket('ws:/localhost:5555');
    ws.onmessage = (frame) => data.push(frame.data);
})();

Is it possible to look up the value of data without stopping the application, or breakpointing onmessage and waiting for it to occur? Is it possible to just look up the value of any variable that I know to be stored persistently somewhere?

Upvotes: 0

Views: 44

Answers (1)

jfriend00
jfriend00

Reputation: 707516

Variables inside a function are private to within that function scope. Only code inside that function scope can examine them.

If you're in the debugger, you will need to be at a breakpoint inside that function scope in order to see that variable.

Sometimes it's appropriate to move the declaration of a variable to a higher scope so that after it is modified inside some local scope, it's value will persist and can be accessed from a higher scope. I don't know what real problem you're trying to solve here to know whether that makes sense for your situation or not.

More likely, since variables like your data variable get modified at some unknown time, the only way some outside code can know when to look at an updated value is by participating in some sort of event system or callback system that notifies outside that it now has a new value. In that case, it's common to just pass the new value to the callback or along with the event. Then the outside code gets the value that way, rather than having to declare it in some parent scope.

Upvotes: 1

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