[Javascript] Immutable opreators

• slice
• filter
• map
• ...spread
• concat
• Object.assign

let items = [1,2,3];

//add
let newItems = [...items, 30];

//remove
var filtered = newItems.filter( item => item !== 2);

//update
let things = [1,2,3,4,5].map(num => ({id: num}));
var i = things.findIndex(item => item.id === 3);
var updated = [
  ...things.slice(0, i),
  {id: 33},
  ...things.slice(i+1)
];


var state = {app: {}, items: [1]};

//add
var newState = Object.assign({}, state, {app: 2, newThings: 2});

// update
var newState = Object.assign({}, state, {app: 2});
var newState = {
  ...state,
  app: 2
};