Interfaces and Types in TS

Function Types TypeScript adding types to functions

There are two different ways in TypeScript how you can specify the structure of your data

We can use Interface and Types

They are very similar, almost everything you can do with the Interface, you can also do with the Type

In TypeScript is recommending to use Interface over Type alias when it's possible

Interface describes data structure in a more natural way

Interface keyword exists only in TypeScript non in vanilla JavaScript. It is helping us to write structured and very explicit code that can help you force classes to have certain features or objects in general to have a specific structure. They allow for optional properties and all optional methods if you add a question mark after the method name

You can't assign a default value inside the Interface, just the property's name, and type

  interface User {
    username: string
    project: string
    years: number

    hello?(name: string): void 

  const userOne: User = {
    username: "slavo3dev",
    project: "NRG Nomad",
    years: 1

Type Alias

  type Username = string
  type PersonLogFunction = (name: string) =>  string 

  const username: string = "Slavo3 NRG Nomad"

  const logUser: PersonLogFunction = (name) => {
    return name;

  const firstUser: Username = logUser(username)