JavaScript examples: No coupling, Loose coupling, Tight coupling

coupling.js

//
// Tight coupling from A to B  => A needs B to be defined, callable and adhere to an interface
// No coupling from B to A     => B does not need A in any way (pure fn)
//
function a() { b() }
function b() {}
a()

//
// No coupling from A to B         => A and B work independently,
//                                     although there a chance of naming collision in `store`
// Tight coupling from A to store  => Direct reference to `store`, mutates original
// Tight coupling from B to store  => Direct reference to `store`, mutates original
//
function a() { store.foo = 'x' }
function b() { store.bar = 'y' }
const store = {}
a()
b()

//
// Loose coupling between A and B   => A and B both operate on the numeric `counter` property,
//                                      although they will not error when it does not exist
// Tight coupling from A to store   => Direct reference to `store`, mutates original
// Tight coupling from B to store   => Direct reference to `store`, mutates original
//
function a() { store.counter = (store.counter || 0) + 1 }
function b() { store.counter = (store.counter || 0) + 10 }
const store = {}
a()
b()

//
// No coupling between A and B     => A and B work independently,
//                                     although there a chance of naming collision in `store`
// Loose coupling from A to store  => Because DI and immutability (pure fn)
// Loose coupling from B to store  => Because DI and immutability (pure fn)
//
function a(store) { return Object.assign({}, store, { foo: 'x' }) }
function b(store) { return Object.assign({}, store, { bar: 'y' }) }
const store0 = {}
const store1 = a(store0)
const store2 = b(store1)