如何在NodeJS应用程序中创建某种上下文，我可以从那里调用的所有函数都可以访问？

Question

In Meteor (a NodeJS Framework), there is a function called Meteor.userId() that always returns the userId that belongs to the current session as long as I am in a function that was original called from a Meteor Method .

The Meteor.userId() function utilizes meteors DDP?._CurrentInvocation?.get()?.connection . So somehow this "Magic line" gets my current DDP connection. This also works when burried deep inside of callbacks.

So somehow meteor sets a context that it refers to. I also want to do this kind of trick for another API that doesn't utilize meteors DDP but is a plain HTTP Api.

What I want to do:

doActualStuff = function(param1, param2, param3) {
    // here, i am burried deep inside of calls to functions
    // but the function at the top of the stack trace was 
    // `answerRequest`. 
    // I want to access its `context` here but without 
    // passing it through all the function calls.
    // What I want is something like this:
    context = Framework.getRequestContext()
}

answerRequest = function(context) {
    //do some stuff
    someFancyFunctionWithCallback(someArray, function(arrayPosition) {
        aFuncCallingDoActualStuff(arrayPosition);
    })
}

I can wrap the call to answerRequest if this is necessary.

Answer 1

I don't know how Meteor does it, but it doesn't look like magic. It looks like Meteor is a global object ( window.Meteor in the browser or global.Meteor in Node.js) that has some functions that refer to some stateful object that exists in the context where they were defined.

Your example could be achieved by having answerRequest (or whatever function calls answerRequest , or whatever you want) call a setRequestContext function that sets the state that will be returned by getRequestContext . If you wanted, you could have an additional function, clearRequestContext , that cleans up after request is over. (Of course, if you have async code you'll need to take care that the latter isn't called until any code that needs that data has finished running.)

This is rudimentary, but it might look something like the below snippet. window.Framework does not need to be defined in the same file as the rest of the code; it just needs to be initialized before answerRequest is called.

 let _requestContext = null; window.Framework = { setRequestContext(obj) { _requestContext = obj; }, getRequestContext() { return _requestContext; }, clearRequestContext() { _requestContext = null; }, }; const doActualStuff = function(param1, param2, param3) { const context = Framework.getRequestContext() console.log('Request context is', context); } const answerRequest = function(context) { Framework.setRequestContext(context); setTimeout(() => { try { doActualStuff(); } finally { Framework.clearRequestContext(); } }, 100); } answerRequest({ hello: 'context' }); 

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