Global variables are almost never a good thing (maybe an exception or two out there...). In this case, it looks like you really just want to export your "name" variable. E.g.,
// module.js
var name = "foobar";
// export it
exports.name = name;
Then, in main.js...
//main.js
// get a reference to your required module
var myModule = require('./module');
// name is a member of myModule due to the export above
var name = myModule.name;
I'm unable to find an scenario where a global var
is the best option, of course you can have one, but take a look at these examples and you may find a better way to accomplish the same:
You need some value that it's the same across the application, but it changes depending on the environment (production, dev or test), the mailer type as example, you'd need:
// File: config/environments/production.json
{
"mailerType": "SMTP",
"mailerConfig": {
"service": "Gmail",
....
}
and
// File: config/environments/test.json
{
"mailerType": "Stub",
"mailerConfig": {
"error": false
}
}
(make a similar config for dev too)
To decide which config will be loaded make a main config file (this will be used all over the application)
// File: config/config.js
var _ = require('underscore');
module.exports = _.extend(
require(__dirname + '/../config/environments/' + process.env.NODE_ENV + '.json') || {});
And now you can get the data like this:
// File: server.js
...
var config = require('./config/config');
...
mailer.setTransport(nodemailer.createTransport(config.mailerType, config.mailerConfig));
// File: constants.js
module.exports = {
appName: 'My neat app',
currentAPIVersion: 3
};
And use it this way
// File: config/routes.js
var constants = require('../constants');
module.exports = function(app, passport, auth) {
var apiroot = '/api/v' + constants.currentAPIVersion;
...
app.post(apiroot + '/users', users.create);
...
Not a big fan of this one, but at least you can track the use of the 'name' (citing the OP's example) and put validations in place.
// File: helpers/nameHelper.js
var _name = 'I shall not be null'
exports.getName = function() {
return _name;
};
exports.setName = function(name) {
//validate the name...
_name = name;
};
And use it
// File: controllers/users.js
var nameHelper = require('../helpers/nameHelper.js');
exports.create = function(req, res, next) {
var user = new User();
user.name = req.body.name || nameHelper.getName();
...
There could be a use case when there is no other solution than having a global var
, but usually you can share the data in your app using one of these scenarios, if you are starting to use node.js (as I was sometime ago) try to organize the way you handle the data over there because it can get messy really quick.
If we need to share multiple variables use the below format
//module.js
let name='foobar';
let city='xyz';
let company='companyName';
module.exports={
name,
city,
company
}
Usage
// main.js
require('./modules');
console.log(name); // print 'foobar'
Save any variable that want to be shared as one object. Then pass it to loaded module so it could access the variable through object reference..
// main.js
var myModule = require('./module.js');
var shares = {value:123};
// Initialize module and pass the shareable object
myModule.init(shares);
// The value was changed from init2 on the other file
console.log(shares.value); // 789
On the other file..
// module.js
var shared = null;
function init2(){
console.log(shared.value); // 123
shared.value = 789;
}
module.exports = {
init:function(obj){
// Save the shared object on current module
shared = obj;
// Call something outside
init2();
}
}
a variable declared with or without the var keyword got attached to the global object. This is the basis for creating global variables in Node by declaring variables without the var keyword. While variables declared with the var keyword remain local to a module.
see this article for further understanding - https://www.hacksparrow.com/global-variables-in-node-js.html
With a different opinion, I think the global
variables might be the best choice if you are going to publish your code to npm
, cuz you cannot be sure that all packages are using the same release of your code. So if you use a file for exporting a singleton
object, it will cause issues here.
You can choose global
, require.main
or any other objects which are shared across files.
Otherwise, install your package as an optional dependency package can avoid this problem.
Please tell me if there are some better solutions.
Not a new approach but a bit optimized. Create a file with global variables and share them by export
and require
. In this example, Getter and Setter are more dynamic and global variables can be readonly. To define more globals, just add them to globals
object.
global.js
const globals = {
myGlobal: {
value: 'can be anytype: String, Array, Object, ...'
},
aReadonlyGlobal: {
value: 'this value is readonly',
protected: true
},
dbConnection: {
value: 'mongoClient.db("database")'
},
myHelperFunction: {
value: function() { console.log('do help') }
},
}
exports.get = function(global) {
// return variable or false if not exists
return globals[global] && globals[global].value ? globals[global].value : false;
};
exports.set = function(global, value) {
// exists and is protected: return false
if (globals[global] && globals[global].protected && globals[global].protected === true)
return false;
// set global and return true
globals[global] = { value: value };
return true;
};
examples to get and set in any-other-file.js
const globals = require('./globals');
console.log(globals.get('myGlobal'));
// output: can be anytype: String, Array, Object, ...
globals.get('myHelperFunction')();
// output: do help
let myHelperFunction = globals.get('myHelperFunction');
myHelperFunction();
// output: do help
console.log(globals.set('myGlobal', 'my new value'));
// output: true
console.log(globals.get('myGlobal'));
// output: my new value
console.log(globals.set('aReadonlyGlobal', 'this shall not work'));
// output: false
console.log(globals.get('aReadonlyGlobal'));
// output: this value is readonly
console.log(globals.get('notExistingGlobal'));
// output: false
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