let a: number;
a = 4;

function sum(a: number,b: number): number{
    return a + b;
}

let x: number = 1;
let y = false;

// &表示同时
let j: {name: string} & {age: number};
j = {name: 'ddd',age: 33};

let n: number | boolean;

// 类型别名
let k: 1 | 2 | 3;

type myType = 1 | 2 | 3;
let m: myType;