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Interface

Interface​

//almost same as type aliases
//use them to create reusable modular types that describe the shape of objects
interface Person{
  name:string;
  age:number;
}
const sayHappyBirthday = (person:Person)=>{
  retun `Hey ${person.name}, congrats on turning ${age}`;
}

sayHappyBirthday({name:'Bob',age:31});

Optional​

interface Person{
  first:string;
  last:string;
  nickname?:string;
}
const tom:Person={first:'tom',last:'page'};

Method​

interface Person{
  readonly id:number;
  first:string;
  last:string;
  nickname?:string;
  sayHi:()=>string;	//accept zero argument and returns a string
}

const p:Person={
	id:222,
	first:'tom',
	last:'Kingston',
	nickname:'tommy',
	sayHi: () =>{return `Hi I am ${this.first}`;}
}

Reopening Interface​

interface File{filename:string;}
interface File{size:number;}
const f:File={filename:'aaa.jpg',size:9}

Extending Interface​

interface File{filename:string;}
interface ImgFile extends File{size:number;}
const f:ImgFile={filename:'aaa.jpg',size:9}

Multiple Extend (multi-inheritance)​

interface Employee{name:string;}
interface Admin{type:string;}
interface User extends Employee,Admin{username:string;}
const a:User={name:'Marilyn',type:'system',username:'mary'}