creating a global object in nodejs accessible by .js modules

Question

My nodejs project requires memory tables accessible by different .js module. Some modules will update the tables but the data must be the same across all modules(sort of a in memory db). As such, I need a truly global object....not a global per module object. Creating a common.js file with all the objects then require it in all the modules will not do since the data will be global/local to the respective modules. I have seen reference to nodejs globals where global.myobject would be global to all modules but the documentation is not clear as to whether this is so or not. The last discussion I saw was from 2014. Can anyone update me on what is the current situation? How is this problem solved?

Having a common.js and exporting an object literal, would be global to all modules that required it.. — Keith
– Keith, Commented Oct 5, 2016 at 23:09
Actually, requiring the same common.js from the other modules will do. Every module is instantiated only once, regardless how often it is required. It's exactly what you need - a singleton. — Bergi
– Bergi, Commented Oct 5, 2016 at 23:09
@Bergi a somewhat similar question stackoverflow.com/questions/8555792/creating-a-global-object from 2011 suggested a singleton but also advised against it. Can you demonstrate how this would work and the pros and cons? — MichaelE
– MichaelE, Commented Oct 6, 2016 at 1:04
@Keith are you saying that by requiring the common.js the changes made to its objects would be reflected in the next module that required it? I am not sure of that. Can you point to some docs that support this? — MichaelE
– MichaelE, Commented Oct 6, 2016 at 1:11
@MichaelE That's a C# question which doesn't really apply here. Yes, a singleton is usually a bad idea exactly because it's global state, but that's what you asked for. Make a module and export an object, it's as simple as that. — Bergi
– Bergi, Commented Oct 6, 2016 at 1:30

Keith · Accepted Answer · 2016-10-06 01:37:39Z

3

In node.js..

if you had a module called common.js, that looked like this..

'use strict';

var obj = {};
module.exports = obj;

And then inside another module you did this

'use strict';
var c = require('./common');
c.test = 1234;

Then later another module did this..

'use strict';
var c = require('./common');
console.log(c);
//output = { test: 1234 }

A module in modejs, is just another object. nodejs, caches any requires, and so will always return the same object.

One gotcha for windows users, windows filenames are not case-sensitive, so if you did require('Common'), and then did require('common'); you would have 2 version of the same module. And this is a good reason to keep all modules names in lowercase.

answered Oct 6, 2016 at 1:37

Keith

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2 Comments

MichaelE Over a year ago

Thanks for the examples...the comments in stackoverflow.com/questions/4140661/… speaks to global.myobject do you have any comments on this alternative

Keith Over a year ago

The problem with global.myobject, is that of scope. The advantage of using a common.js file would be it's a global that's scoped to your modules's.. If for some reason there were other third party library's that wanted to share info, then the global.myobject could maybe be used. IOW: The global is a bit like browsers window object.

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