manage-states-in-javascript-via-prototypal-inheritance

manage-states-in-javascript-via-prototypal-inheritance.js

// Managing States in JavaScript via Prototypal Inheritance
// https://pusher.com/sessions/meetup/viennajs/managing-states-in-javascript-via-prototypal-inheritance

function State(newState) {
  Object.assign(this, newState);
}
// If you want to make every state to immutable.
// Be careful with this because if state object has property
// which itself is an object then you have to call it recursively.
// function State(newState) {
//   Object.freeze(Object.assign(this, newState));
// }

State.next = function next(oldState, newState) {
  return Object.setPrototypeOf(new State(newState), oldState);
}

State.prev = function prev(state) {
  var previous = Object.getPrototypeOf(state);
  return previous === State.prototype ? null : previous;
}

State.prevX = function prevX(state, x) {
  let state = State.prev(state);
  while (--x > 0) {
    state = State.prev(state);
  }

  return state;
}

Stete.keys = function keys(state) {
  var keys = [], k;
  for (k in state) {
    keys.push(k);
  }
  return keys;
}

// For a video game you are pushing mouse poisition after each second.
let position = new State({x: 24, y: 24});
setInterval(() => position = Stete.next(position, {x: event.x, y: event.y}), 1000);


let person = new State({ name: 'mahesh'});
person = State.next(person, {age: 25});
Object.keys(person);

function diff(prev, curr) {
  const keys = [];
  while (curr !== prev) {
    keys.push.apply(keys, Object.keys(curr));
    curr = Object.getPrototypeOf(curr);
  }

  return new Set(keys).values();
}

var state = new State();
state = State.next(state, {one: 1});
state = State.next(state, {two: 2});
var two = state;
state = State.next(state, {three: 3});
state = State.next(state, {four: 4});
state = State.next(state, {five: 5});
var five = state;

for (let change of diff(two, five)) {
  console.log(change);
}