We’ve seen types for basic values.

For more complex structures we can use type aliases:

type Dog = {
  name: string
  age: number
}

Then when you create an object, you set this to be its type:

const jack: Dog = {
  name: 'Jack',
  age: 3
}

Note that we can have an optional property using ?: when defining it, like this:

const jack: Dog = {
  name: 'Jack',
  age?: 3 //optional
}

To do the same thing we can also use interfaces:

interface Dog {
  name: string
  age: number
}

They work in the same way as type aliases:

const jack: Dog = {
  name: 'Jack',
  age: 3
}

Why use one vs another? There are a few differences, but generally you can use one, or another, no big deal.

Type aliases or interfaces are not limited to typing objects, of course:

interface Pair {
  a: number;
  b: number;
}

const multiply = (nums: Pair) => {
  return nums.a * nums.b
}

multiply({ a:1, b: 2 })

If you pass a third parameter, TS will raise an error:

“Object literal may only specify known properties, and c does not exist in type Pair”

Lessons this unit:

0:	Introduction
1:	Your first TypeScript program
2:	Types
3:	Typing functions
4:	The editor helps you with type errors
5:	Running TypeScript code
6:	Valid types
7:	▶︎ Type aliases and interfaces
8:	Union types
9:	Typing arrays with generics
10:	The DX of editing TypeScript
11:	There's more...
12:	tsconfig.json COMING SOON
13:	Installing types COMING SOON