Modules

Fancy word for a file/folder that contains code.

Node Modules

arguments keyword:

function func() { console.log(arguments) }
func(3, 4, 5, 6)

Node is not only executing a line of code, it actually wraps the file with a function:

console.log(arguments); // suppose this is at top level of the file

it's actually like this:

function _(exports, module, require, __filename, __dirname) {
  console.log(arguments);
  return module.exports;
}

We usually use exports keyword to export things, it's actually not a global keyword or something, it's just the first argument to the hidden wrapping function. Also, variables declared at top level are not global as well.

Browser don't like Node, it doesn't have hidden wrapping function, so variables declared at top level is global.

exports is just alias of module.exports.

(exports, module, ...) { // Node does this wrap (module.exports, module, ...)
  exports.a = 1
  module.exports.b = 99
  // if we do like this, we're not changing the module object, we just assign new pointer that no longer point to module.exports
  exports = ...
  exports = () => {}  // break the assignment reference
  module.exports = () => {}  // ok because module.exports is actually what is being returned
}

Types of API objects

Object

Top-level API is a simple object. So, no need to use module.exports

exports.name = 'Tu'
exports.age = 23

const me = require('./me')
console.log(me.name, me.age)

Array, String, Function

Use module.exports.

module.exports = [2, 3, 4, 7]

Global Object

setTimeout()  // implies global.setTimeout()

You can actually make object globally by attaching it to global.

warning

Avoid doing that!

Errors & Exceptions

Error is "problem", exception is "condition".