ts基础类型及其用法

1、string

// 普通字符串、模版字符串
let name: string = "bob";
let sentence: string = `Hello, my name is ${ name }.`

2、number

//支持十进制、十六进制、二进制、八进制
let decLiteral: number = 6;
let hexLiteral: number = 0xf00d;

3、boolean

let isHot:boolean=true

4、数组

let list:number[]=[1, 2, 3] //类型+[]
let list:Array<number>=[1,2,3]  //数组泛型，Array<元素类型>：

5、元祖（已知元素类型和数量的数组）

let x: [string, number];
x = ['hello', 10]; //索引类型必须对上
x= [10,'hello'];//报错
//当访问越界的元素，会使用联合类型替代：
x[3] = 'world'; // OK, 字符串可以赋值给(string | number)类型
console.log(x[5].toString()); // OK, 'string' 和 'number' 都有 toString
x[6] = true; // Error, 布尔不是(string | number)类型

6、枚举

//默认编号从0开始
enum Color {Red, Green, Blue}
let c: Color = Color.Green;
//手动设置编号
enum Color {Red = 1, Green = 2, Blue = 4}
let c: Color = Color.Green;
//由枚举的值得到它的名字
enum Color {Red = 1, Green, Blue}
let colorName: string = Color[2];
console.log(colorName) //Green

7、any

let notSure: any = 4;
let list: any[] = [1, true, "free"];
list[1] = 100;

8、void

//通常表示函数没有返回值
function warnUser(): void {
    alert("This is my warning message");
}
//声明一个void变量，它的值只能是null或者undefined
let unusable: void = undefined;

9、null和undefined

let u: undefined = undefined;
let n: null = null;

10、Never

// 返回never的函数返回错误
function error(message: string): never {
    throw new Error(message);
}
// 返回never的函数必须存在无法达到的终点
function infiniteLoop(): never {
    while (true) {
    }
}

11、断言

//尖括号
let someValue: any = "this is a string";
let strLength: number = (<string>someValue).length;
//as
let someValue: any = "this is a string";
let strLength: number = (someValue as string).length;