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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 the type, like this:
type Dog ={
name: string,
age?: number //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”