How to access global scope variables in callback functions? [JS]

Question

For my user registration I have

const express = require ('express');
const userRouter = express.Router ();

userRouter.get ('/', function getUserList (req, res) {
    let User = require ('../models').User;
    User.find ({}, function (err, list) {
        res.json (list);
    });
});

userRouter.post ('/', function createUser (req, res) {
    let User = require ('../models').User;
    if (req.body.username && req.body.password)
        User.create (req.body, function (err, user) {
            res.json (user);
        });
});

... 3 more functions with the same `let User` ...

module.exports = userRouter;

Here, I have to require the module models twice. I tried setting the User variable as a global variable up at the top of the program, like

const express = ..., userRouter = ...
var User = ...

However this User variable is still not accessible inside my callback functions.

Is requiring the User module multiple times the correct way to do this or am I missing something?

edit: Inside the callback functions, the User variable is undefined.

no reason it shouldn't be accessible when declared outside the callbacks. What errors occur? — charlietfl
– charlietfl, Commented Apr 28, 2018 at 11:42
global.User = ... stackabuse.com/using-global-variables-in-node-js — Doug
– Doug, Commented Apr 28, 2018 at 11:48
@Doug Was going to post that but you mentioned it first so I think you should post that as an answer. — AndrewL64
– AndrewL64, Commented Apr 28, 2018 at 11:50

AndrewL64 · Accepted Answer · 2018-04-28 13:09:05Z

1

As @Doug mentioned, you should pass global to the user variable like this:

global.user = ...

This process essentially turns user into a globally accessible variable. You can read more about Node's global here to understand what it does as well as understand what it's implications are too: http://stackabuse.com/using-global-variables-in-node-js/

edited Apr 28, 2018 at 13:09

answered Apr 28, 2018 at 12:11

AndrewL64

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4 Comments

Bergi Over a year ago

No, you should not use a global variable. A module-level constant should be enough.

AndrewL64 Over a year ago

@Bergi agreed. That is mentioned in the link I provided too. But they also showed which situations may require global variable to be used.

Bergi Over a year ago

Yes, I'm just saying that this is not one of these situations.

vixrant Over a year ago

This would make my User variable accessible throughout all modules right? I don't want that, I want it to be accessible in the callbacks of the same module. Which isn't happening because the callbacks are saying that User variable is undefined.

vredrav · Accepted Answer · 2018-04-28 15:29:27Z

1

To @charloetfl ‘s point if it is just within the file, declaring it outside the callback or on top of the file should do. If we are talking about access across all modules and files within the project then adding it to the global object is the way to go about it in node as @doug and @andrewl mentioned.

edited Apr 28, 2018 at 15:29

answered Apr 28, 2018 at 14:11

vredrav

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2 Comments

vixrant Over a year ago

Declaring User outside leads to callback functions saying the User variable is undefined.

vredrav Over a year ago

As using global is also not recommended in node development, I would recommend looking in to creating the User variable within app.locals so it would be accessible in your req object through req.app.locals as described in expressjs.com/en/api.html#app.locals. Hope this helps.

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