Once we’ve defined an object, we’re not stuck with all the properties we wrote. Objects are mutable meaning we can update them after we create them!

We can use either dot notation, ., or bracket notation, [], and the assignment operator, = to add new key-value pairs to an object or change an existing property.

One of two things can happen with property assignment:

• If the property already exists on the object, whatever value it held before will be replaced with the newly assigned value.
• If there was no property with that name, a new property will be added to the object.

It’s important to know that although we can’t reassign an object declared with const, we can still mutate it, meaning we can add new properties and change the properties that are there.

const spaceship = {type: 'shuttle'};
spaceship = {type: 'alien'}; // TypeError: Assignment to constant variable.
spaceship.type = 'alien'; // Changes the value of the type property
spaceship.speed = 'Mach 5'; // Creates a new key of 'speed' with a value of 'Mach 5'

You can delete a property from an object with the delete operator.

const spaceship = {
  'Fuel Type': 'Turbo Fuel',
  homePlanet: 'Earth',
  mission: 'Explore the universe' 
};

delete spaceship.mission;  // Removes the mission property