module.exports vs exports

module.exports vs exports

We see module.exports and exports often, what are the differences?

Create a file module.js:

console.log(exports === module.exports);
console.log(exports);

Run in command line:

$ node module.js
true
{}

=== return true, it means they both point to the same null object{}.

Then, when should I only use module.exports? and when should I only use exports? From the perspective of the module developer, there is no difference; the only difference probably is that exports is 7 characters less than module.exports. However, from the perspective of module users, there is a difference between these two.

exports.pi = 3.14;
// vs
module.exports.pi = 3.14;

Anonymous function

Assume I, as a module user, want to import a function in my code:

const func = require ('./ module');

then the developer can only use module.exports to define the function:

module.exports = function () {}

What if the developer uses exports to define:

exports.func = function () {}

In that case, the user must know the name of the function to use:

const {func} = require ('./ module');

The same goes for replacing functions with variables, constants or other types of data.

Attention object

As I mentioned earlier, module.exports and exports point to the same null object {} and we call it M. That is to say, no matter if it is exports.pi = 3.14 or module.exports.pi = 3.14, we are to operate the M objects. As we know, in Node / JavaScript, the objects are alterable and can be modified at will.

Therefore, we can directly assign values ​​to exports:

exports = 3.14;

But in that case, exports means nothing at all because it would no longer to points to the object M after variable assignment, so it cannot operate the M object, and cannot control the data which is to be exported by the module, so this operation is wrong and should be avoided.

What about assigning a value to module.exports?

module.exports = 3.14;

There is no problem, the module exports a value by default, not the M object.

To sum up, in Node.js module, the exports is shortcut for referencing module.exports, if your module is to export an object. It is a pretty much useless object if your module exports any other data type, such as strings, values , Functions, etc., or you have assigned anything to module.exports.