- 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
};