Typescript type

 type Common writing method of ：

// not used type
let sum:(x:number,y:number) => number
sum=(x,y)=>x+y
const result = sum(1,2)
console.log(result)


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

// type Union type 
type strOrNum=string|number
let result3:strOrNum='12'
result3=12

// More commonly used 
type Directions='Up'|'Down'|'Left'|'Right'
let toWhere:Directions='Down'

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