oop.txt

Object Oriented Programming

I   Objects / Classes are main units of design
II  Objects are namespaces (expression problem, duality with Functional Programming)
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
III  Delegation / Inheritance (type dependency)
 IV  Constructors (vs data constructors)
  V  Mutability (shared state)
 VI  Fluent API (http://paqmind.com/blog/fluent-api-debunked/)
VII Instance

http://paqmind.com/blog/dialogue-with-oop-guy/

oop1.js

// === MANUAL DELEGATION ===

// I
let User = {
  name: "",
  role: "",
  getName: function () {
    return this.name
  },
  dataType: "user", // "constant" field
}

let Admin = {
  name: "",
  role: "admin",
  prototype: User,
}

function makeUser({name, role}) {
  return Object.assign(
    {}, User, {name: name, role: role}
  )
}

function makeAdmin({name}) {
  return Object.assign(
    {}, Admin, {name: name}
  )
}

let user = makeUser({name: "Alice", role: "manager"})
let admin = makeAdmin({name: "Bob"})

// console.log(user.getName())  // Alice
// console.log(admin.getName()) // TypeError: admin.getName is not a function

// II
// function withDelegation(method, object) {
//   if (object[method]) {
//     return object[method].call(object)
//   } else {
//     throw Error("delegation is not implemented (yet)")
//   }
// }
//
// console.log(withDelegation("getName", user))  // Alice
// console.log(withDelegation("getName", admin)) // Error: delegation is not implemented (yet)

// III
function get(propName, obj) {
  if (propName in obj) {
    return obj[propName]
  } else if (obj.prototype) {
    return get(propName, obj.prototype)
  } else {
    throw Error(`Cannot read property '${propName}' of ${obj}`)
  }
}

function call(propName, object) {
  let propValue = get(propName, object)
  return propValue.call(object)
}

console.log(call("getName", user))  // Alice
console.log(call("getName", admin)) // Bob
console.log(get("dataType", user))  // user
console.log(get("dataType", admin)) // user

oop2.js

// === AUTO DELEGATION ===

// I
let User = {
  name: "",
  role: "",
  getName: function () {
    return this.name
  },
  dataType: "user", // "constant" field
}

let Admin = Object.assign(Object.create(User), {
  name: "",
  role: "admin",
  prototype: User,
})

function makeUser({name, role}) {
  return Object.assign(
    Object.create(User), User, {name: name, role: role}
  )
}

function makeAdmin({name}) {
  return Object.assign(
    Object.create(Admin), Admin, {name: name}
  )
}

let user = makeUser({name: "Alice", role: "manager"})
let admin = makeAdmin({name: "Bob"})

console.log(user.getName())  // Alice
console.log(admin.getName()) // Bob
console.log(user.dataType)   // user
console.log(admin.dataType)  // user

oop3.js

// === AUTO INSTANTIATION ===

// I
function User({name, role}) {
  this.name = name
  this.role = role
  return this
}

User.prototype.getName = function () {
  return this.name
}

User.prototype.dataType = "user" // "constant" field

function Admin({name}) {
  this.name = name
  this.role = "admin"
}

Admin.prototype = Object.create(User.prototype)

let user = new User({name: "Alice", role: "manager"})
let admin = new Admin({name: "Bob"})

console.log(user.getName())  // Alice
console.log(admin.getName()) // Bob
console.log(user.dataType)   // user
console.log(admin.dataType)  // user

oop4.js

// === SYNTAX SUGAR ===

// I
class User {
  constructor({name, role}) {
    this.name = name
    this.role = role
  }

  getName() {
    return this.name
  }

  // static dataType = "user" // doesn't work (yet?!)
}

User.prototype.dataType = "user" // "constant" field

class Admin extends User {
  constructor({name, role}) {
    super({name: name, role: "admin"})
  }
}

let user = new User({name: "Alice", role: "manager"})
let admin = new Admin({name: "Bob"})

console.log(user.getName())  // Alice
console.log(admin.getName()) // Bob
console.log(user.dataType)   // user
console.log(admin.dataType)  // user