Objects: labeled data

Objects are JavaScript's dictionaries

Arrays handle many-of-the-same-thing; objects handle one-thing-with-many-facts. A user has a name, an age, a plan; a product has a title and a price. Nearly every piece of data a server will ever send you (lesson 5-3) arrives in this shape, so reading and writing it has to become reflex.

An array numbers its items. An object names them. It is JavaScript's version of the Python dict you used for labeled data:

const user = {
  name: "Ada",
  age: 36,
  premium: true
};

Each name: value pair is a property. Unlike Python dicts, the keys are written without quotes (they are allowed, just not needed for normal names).

Reading has two spellings:

• Dot notation, the everyday one: user.name
• Bracket notation, for keys stored in variables or keys with odd characters: user["age"] or user[someKey]

Writing works the same way. Assigning to a property that does not exist yet simply creates it, and delete user.premium removes one. Like arrays, a const object can still have its contents changed.