What do “module.exports” and “exports.methods” mean in NodeJS / Express?

Question

Looking at a random source file of the express framework for NodeJS, there are two lines of the code that I do not understand (these lines of code

Answer 1

You can find the best answer in node.js source code. If someone is requiring your js module, your script turns into a function by node as follows (see src/node.js).

// require function does this..
(function (exports, require, module, __filename, __dirname) {
    ... your javascript contents...
});

Node will wrap your script. Then above script will be executed as follows:

//module.js
var args = [self.exports, require, self, filename, dirname];
return compiledWrapper.apply(self.exports, args);

So in your script,

exports is just module.exports.

In your script, you can add something to this exports object (functions..). require function will return this object. This is node.js's module system (commonJS specification).

But be careful not to modify module.exports. Otherwise your current exports will be meaningless.