Node modules that instantiate things?

Question

Can I build a module that exports instantiated variables?

Module:

var module1 = require('module1')
var Module2 = require('module2')

module1.dosomething(variables)
exports.module1 = module1

//or

module2 = new Modle2(variables)
module2.dosomething(variables)
exports.module2 = module2

Can I require the module above in many other files and use the exports as instantiated variables or will they be re-instantiated every time I require them and not shared between the files requiring them.

Thanks!

You can do either. Not a good answer. It depends on how you want to do it. — Jamund Ferguson, May 18 '12 at 21:53
I can do both of those and the exports wont be re-instantiated versons of module1 and module2 each time they are required? The exports will always refer to the already instantiated versions? — fancy, May 18 '12 at 21:55
It depends, but yes, see my answer to this other question http://stackoverflow.com/questions/8931239/how-to-access-variables-declared-in-main-app-js-in-seperate-route-files-in-node/8931366#8931366 — Jamund Ferguson, May 18 '12 at 21:56

kmiyashiro · Accepted Answer · 2013-01-12T02:29:29.783

Your example is confusing because you use module1 in multiple contexts, both as a module, a variable within another module, and an exported property of that module.

Think of modules as closures and exports as return values. Most likely you want to export a function/factory function and call that every time if you want to create new instances with the export, anything else will be shared since it just returns the object.

Module1

module.exports.var1 = function(opts) {
    // do stuff
    return variables;
};

module.exports.var2 = new Blah(); // single instance

Other module

var var1 = require('module1').var1({ opt1: 'foo' }); // New instance every time
var var2 = require('module1').var2; // Same var instance even if you include in another module

score 1 · Answer 2 · answered May 18 '12 at 22:08

1

You can even do things like this to be really annoying. Most npm modules make you create instantiated versions to avoid this kind of silliness.

// file.js
var m1 = require('./m1');
m1.awesome = false;
console.log("I am awesome", m1.awesome);

// file2.js
var m1 = require('./m1');
console.log("I am awesome", m1.awesome);

// both.js
require('./file');
require('./file2');

// m1.js
exports.awesome = true;

now run this:

node file1.js
I am awesome false

node file2.js
I am awesome true

node both.js
I am awesome false
I am awesome false

answered May 18 '12 at 22:08

Jamund Ferguson

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This basically means in both.js the file1's operations polluted file2 operations right? Meaning we should always export objects that can be instantiated? – CMCDragonkai Mar 06 '14 at 13:58
If you return a new object either by doing `new` or by using the factory pattern then yeah you can't collide. – Jamund Ferguson Mar 06 '14 at 17:54

Node modules that instantiate things?

2 Answers2