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

let items = [1,2,3];//addlet newItems = [...items, 30];//removevar filtered = newItems.filter( item => item !== 2);//updatelet 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]};//addvar newState = Object.assign({}, state, {app: 2, newThings: 2});// updatevar newState = Object.assign({}, state, {app: 2});var newState = {  ...state,  app: 2};