Avoiding Object mutations with Object.assign() and ...spread

Shows the naive toggleTodo implementation

  const toggleTodo = (todo) => {
  todo.completed = !todo.completed;
  return todo;
}

Instead, to not to mutate, the object, but still keep the function generic:

  return Object.assign({}, todo, {
  completed: !todo.completed
});

Here (above), he passes an empty object to assign, to make sure to not to mutate the data (Object.assign({}....

Then you add several objects to merge into this empty object. Here there's todo and the property we want to override.

Abundancia