module.exports vs exports in Node.js

Question

I\'ve found the following contract in a Node.js module:

module.exports = exports = nano = function database_module(cfg) {...}

I wonder what

Answer 1

I went through some tests and I think this may shed some light on the subject...

app.js:

var ...
  , routes = require('./routes')
  ...;
...
console.log('@routes', routes);
...

versions of /routes/index.js:

exports = function fn(){}; // outputs "@routes {}"

exports.fn = function fn(){};  // outputs "@routes { fn: [Function: fn] }"

module.exports = function fn(){};  // outputs "@routes function fn(){}"

module.exports.fn = function fn(){};  // outputs "@routes { fn: [Function: fn] }"

I even added new files:

./routes/index.js:

module.exports = require('./not-index.js');
module.exports = require('./user.js');

./routes/not-index.js:

exports = function fn(){};

./routes/user.js:

exports = function user(){};

We get the output "@routes {}"

---

./routes/index.js:

module.exports.fn = require('./not-index.js');
module.exports.user = require('./user.js');

./routes/not-index.js:

exports = function fn(){};

./routes/user.js:

exports = function user(){};

We get the output "@routes { fn: {}, user: {} }"

---

./routes/index.js:

module.exports.fn = require('./not-index.js');
module.exports.user = require('./user.js');

./routes/not-index.js:

exports.fn = function fn(){};

./routes/user.js:

exports.user = function user(){};

We get the output "@routes { user: [Function: user] }" If we change user.js to { ThisLoadedLast: [Function: ThisLoadedLast] }, we get the output "@routes { ThisLoadedLast: [Function: ThisLoadedLast] }".

---

But if we modify ./routes/index.js...

./routes/index.js:

module.exports.fn = require('./not-index.js');
module.exports.ThisLoadedLast = require('./user.js');

./routes/not-index.js:

exports.fn = function fn(){};

./routes/user.js:

exports.ThisLoadedLast = function ThisLoadedLast(){};

... we get "@routes { fn: { fn: [Function: fn] }, ThisLoadedLast: { ThisLoadedLast: [Function: ThisLoadedLast] } }"

So I would suggest always use module.exports in your module definitions.

I don't completely understand what's going on internally with Node, but please comment if you can make more sense of this as I'm sure it helps.

-- Happy coding