Add function to external module in nodejs

Question

I need a function in main.js (the script that is running) to be recognized in the scope of the modules:

Modules.js:

function x(){
     functionNeeded();
}

module.export.x = x;

Main.js

var m = require("modules.js");

function functionNeeded(){
     //function needed to call
}

//m.x() is called successfully
//but fails because functionNeeded is not defined (check modules.js)
//with m.functionNeeded = functionNeeded before calling m.x() it also fails.

Does anyone have any idea on how can this achieve so I can spread a function of main.js across several modules without duplicating it or spreading it across the modules?

Why not put that function in it's own module, and require it where you need it. The alternative would be to just pass it as an argument. — adeneo
– adeneo, Commented Oct 2, 2016 at 18:16
Without changing module.js, you can't do this. module.js runs in its own scope and you can't change that scope from outside of module.js (for good reason) except messing with globals which is never a good idea. You could, of course, edit module.js to solve this issue in many ways (the most flexible would be to put functionNeeded() in its own module which module.js can require() in or you can pass it in to x() as a callback. — jfriend00
– jfriend00, Commented Oct 2, 2016 at 18:46

Frank Bessou · Accepted Answer · 2016-10-02 18:21:41Z

2

You can provide your function to the module by passing it as argument:

Module.js:

function x(functionNeeded){
     functionNeeded();
}

module.export.x = x;

Main.js

var m = require("modules.js");

function functionNeeded(){
     //function needed to call
}

m.x(functionNeeded)

answered Oct 2, 2016 at 18:21

Frank Bessou

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Comments

Jacob · Accepted Answer · 2016-10-02 18:23:47Z

0

I'd really not recommend this, but you do have global available to you in node:

global.functionNeeded = function () {
};

...but:

You'd have to make sure your initialization runs before anything referencing that function.
This makes your code hard to reason about; it's not explicit where that function comes from or when it becomes available.

It is much better to just require your function in every module that relies on it.

answered Oct 2, 2016 at 18:23

Jacob

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2 Comments

Fane Over a year ago

Is there any problem with recursive requires if I call several modules which each one has its own require?

Jacob Over a year ago

No; nodejs has a module cache; the module will only be evaluated the first time it's required, then stored in the cache; afterward, when that same module is required, you'll get back a reference to that same module object.

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