Day 5 - Interfaces and Type Aliases

Interfaces

Interfaces are a way to define a structure that other data structures can adhere to. They can be classes, object literals, etc.

We can simply define an interface as follows:

interface Author {
    name: string,
    avatar: string
}

//using an interface
const authorOne: Author = {name: "mario", avatar: "/image/mario.png"}

We can also use interfaces as types inside other interfaces

interface Post {
    title: string,
    body: string,
    tags: string[],
    created_at: Date,
    author: Author //Here we are using previously created Author interface.
}

const newPost: Post = {
    title: "new Title",
    body: "New Body",
    tags: ["gemini", "trends"],
    created_at: new Date(),
    author: authorOne //Author object created previously
}

We can also pass interfaces as argument types in our functions

function createPost(post: Post): void {
    console.log(`post says ${post.title}, by ${post.author.name}`);
    return;
}

Interfaces can be treated as datatypes in ts. Once we create them all the properties are followed through. You can even create arrays of interfaces to be used when needed.

Type Aliases

Type aliases are pretty similar to interfaces but there is a difference in how to define them.

Type Rgb = [number, number, number]

//it can also be an object
Type user = {
    name: string
    score: number
}

From this point on it is the same as the interface. you define functions, pass them in as arguments, etc just like in interfaces.