TypeScript中type和interface的区别及注意事项

type AliasName = Type;

interface InterfaceName {
  TypeMember;
  TypeMember;
  ...
}

type Shape = { name: string }

type Circle = Shape & { radius: number }

function foo(circle: Circle) {
  const name = circle.name
  const radius = circle.radius
}

type NumericType = number | bigint;

interface Circle {
  radius: number;
}

function f(value: NumericType, circle: Circle) {
  const bar: boolean = value;
  //    ~~~
  // 	  Type 'number | bigint' is not assignable to type 'boolean'
  // 		这里没有显示类型别名
  
  const baz: boolean = circle;
  // 	  ~~~
  // 		Type 'Circle' is not assignable to type 'boolean'
}

type user=string
//接收一个字符串类型的数据，返回一个user类型(字符串类型)的数据
function Input(str:string):user{
    return str.slice(0,2)
}
//把返回结果赋值给userInput
let userInput=Input('hello')
//重新给其赋值一个字符串类型的值,没有报错,说明用type声明的字符串类型生效
userInput='new'

interface Point{
    x:number,
    y:number
}
//接收一个Point的对象类型数据
function printCoord(pt:Point){
 
}
//给函数传一个对象类型的数据，没有报错,说明用interface声明的类型生效
printCoord({
    x:100,
    y:100
})

//扩展接口
interface Animal{
    name:string
}
interface Bear extends Animal{
    honey:boolean
}
//声明一个类型为Bear类型的对象，要求既要有name，也要有honey。说明用extends扩展接口成功
const bear:Bear={
    name:'winie',
    honey:true
}
console.log(bear.name);
console.log(bear.honey);

//扩展类型
type Animal={
    name:string
}
//给Animal扩展接口
type Bear=Animal&{
    honey:boolean
}
const bear:Bear={
    name:'winie',
    honey:true
}

//向现有的类型添加新字段
interface MyWindow{
    title:string
}
interface MyWindow{
    count:number
}
const w:MyWindow={
    title:'wz',
    count:666
}

//类型创建后不能更改
type MyWindow={
    title:string
}
type MyWindow={
 
}

type FType = boolean | string | number;