When to use module.exports or exports in Node.js?

By nature both exports and module.exports point to the same object. So if you add properties to one of them both will receive this property because they point to the same object.

In practice what NodeJS (CommonJS modules) does is:

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

// aqui escreves o código no ficheiro do modulo.
// as linhas que eu coloquei aqui (antes e depois) o NodeJS faz automáticamente
// e nem precisas de as escrever ou pensar nelas

return module.exports;

So if you create a new property in module.exports it will be accessible via exports because they point to the same object. That is:

module.exports.foo = 'bar';
console.log(exports.foo); // 'bar'

There is, however, one crucial difference: you must take into account that when you request a module what is returned is module.exports . This means that if you re-assign module.exports to a new value, object, or function, require will not reference this. For example within a script.js file if you have this code:

console.log(module.exports == exports); // dá true
module.exports = 'foo';
exports = 'bar';

So when you do require of this module, what is exported is module.exports and not export , because you re-assigned new values to these variables / properties and by nature of the NodeJS / CommonJS what is exported is module.exports . So you'll get this:

var foo = require('./script.js');
console.log(typeof foo, foo);          // string 'foo', e não 'bar' que tinhas defenido no exports

If you want to use modules you should export with module.exports . If you want to export more than one function / object / variable you must do:

module.exports = {
    get: function(){ ... },
    set: function(){ ... }
}