typescript的type

 type的常用写法：

//未使用type
let sum:(x:number,y:number) => number
sum=(x,y)=>x+y
const result = sum(1,2)
console.log(result)


//使用type
type PlusType=(x:number,y:number)=>number
let sum2:PlusType=(x,y)=>x+y
const result2=sum2(2,3)
console.log(result2)

// type结合联合类型
type strOrNum=string|number
let result3:strOrNum='12'
result3=12

//比较常用
type Directions='Up'|'Down'|'Left'|'Right'
let toWhere:Directions='Down'

//type结合接口
interface IName{name:string}
type IPerson=IName&{age:number}
let person:IPerson={name:'jim',age:123}