1. let num: number = 10
    2. let flag: boolean = true
    3. let str: string = 'yingximu'
    4. let un: undefined = undefined
    5. let nu: null = null
    6. let strs: string[] = ['ying', 'xi']
    7. let nums: number[] = new Array(1, 2)
    9. function sum(num1: number, num2: number): number {
    10.   return num1 + num2
    11. }
    13. const fun = (num1: number, num2: number) => num1 + num2
    15. let person: {
    16.   name: string
    17.   age: number
    18.   sayHi: () => void
    19. }
    21. person = {
    22.   name: 'yingximu',
    23.   age: 18,
    24.   sayHi: () => {
    25.     console.log('function')
    26.   },
    27. }