05-immutability.md

Immutability

As alluded to in the intro, immutability also makes sense in Javascript.

Use Object.assign or the Object Spread Operator

The idea is to create shallow copies of objects. For example, the code below returns an object that's a shallow copy of the todos (that's what the object spread operator does), then overrides the todo with the latest copy.

function updateTodo(todos, todo) {
  return {...todos, [todo.id]: todo}
}

This approach is perfect for toy apps and quick prototypes. One drawback is that it's error prone---it is very easy to forget to use Object.assign/the spread operator, and the code still works until it throws weird bugs. The other issue is that you're creating shallow copies of objects--- this quickly becomes inefficient as soon as your data grows.

Use an Immutable Library

ImmutableJS is easy to use and performant. It's also very popular.