TypeScript教程--ts数据类型

TypeScript教程

ts数据类型

说明：ts中数据类型包括js已有的数据类型、ts新增的数据类型，本文讲解ts新增的数据类型。

• any

• unknown

• never

• void

• tuple

• enum

• type

一、any

说明：任意类型（相当于关闭类型检查）

1.显式any

let any1: any
console.log("any1 type:", typeof any1) //any1 type: undefined
any1 = 1
console.log("any1 type:", typeof any1) //any1 type: number
any1 = true
console.log("any1 type:", typeof any1) //any1 type: boolean
any1 = "a"
console.log("any1 type:", typeof any1) //any1 type: string
let str_any1: string
str_any1 = any1;
console.log("any1/2 value:", any1 / 2)
//any1=1 any1/2 value:0.5; any1:true any1/2 value:0.5; any1:"a" any1/2 value: NaN;

2.隐式any

let any2
console.log("any2 type:", typeof any2) //any2 type: undefined
any2 = 1
console.log("any2 type:", typeof any2) //any2 type: number
any2 = true
console.log("any2 type:", typeof any2) //any2 type: boolean
any2 = "a"
console.log("any2 type:", typeof any2) //any2 type: string

备注：未声明变量类型且未设置默认值

二、unknown

说明：未知类型（相当于类型安全的any）

let unknown1: unknown
console.log("unknown1 type:", typeof unknown1) //unknown1 type: undefined
unknown1 = 1
console.log("unknown1 type:", typeof unknown1) //unknown1 type: number
unknown1 = true
console.log("unknown1 type:", typeof unknown1) //unknown1 type: boolean
unknown1 = "a"
console.log("unknown1 type:", typeof unknown1) //unknown1 type: string
let str_unknown1: string
//str_unknown1=unknown1; //TS2322: Type unknown is not assignable to type string
if (typeof unknown1 === 'string') {
    str_unknown1 = unknown1;
}
str_unknown1 = unknown1 as string
str_unknown1 = <string> unknown1
//console.log("unknown1/2 value:",unknown1/2) //TS18046: unknown1 is of type unknown
if (typeof unknown1 === 'number') {
    console.log("unknown1/2 value:", unknown1 as number / 2)
}
console.log("unknown1/2 value:", unknown1 as number / 2)
console.log("unknown1/2 value:", <number> unknown1 / 2)
//unknown1=1 unknown1/2 value:0.5; unknown1:true unknown1/2 value:0.5; unknown1:"a" unknown1/2 value: NaN;

备注： any任意类型，相当于关闭类型检查；unknown未知类型，仍然会进行类型检查。

三、never

说明：不存在值所属的类型（0,false,'',undefined,null等任何类型都不能赋值给never）

let never1: never
//never1=undefined; //TS2322: Type undefined is not assignable to type never
//never1=null; //TS2322: Type null is not assignable to type never

function throwError(message: string): never {
    throw new Error(message);
}

function handleStatus(status: 1 | 2 | 3) {
    switch (status) {
        case 1:
            console.log('状态1');
            break;
        case 2:
            console.log('状态2');
            break;
        //case 3:
            //console.log('状态3');
            //break;
        default:
            //前置类型检查是否已涵盖全部状态
            const check: never = status; //TS2322: Type number is not assignable to type never
            throw new Error(`异常状态: ${status}`);
    }
}

四、void

说明：没有任何类型值的特殊类型

let void1: void
//void1=null; //TS2322: Type null is not assignable to type void
void1 = undefined;
//应用举例
function sayHello(): void {
    console.log("Hello, world!");
    //return; //可选
    //return undefined; //可选
    //return "Hello"; //TS2322: Type string is not assignable to type void
}

let void_result = sayHello();
//if(void_result){ //TS1345: An expression of type void cannot be tested for truthiness.
	//console.log(void_result)
//}

备注：如果一个函数没有显式地指定返回类型，且没有return或return没有指定返回，那么该函数的返回类型会被隐式地推断为undefined。

五、tuple

说明：一种特殊类型数组，其中元素具有多类型、有序性的特点，存储一定数量的元素。

let tuple1: [string, number, boolean]
tuple1 = ["a", 1, true]
tuple1[2] = false
//可选参数
let tuple2: [string, number, boolean?]
tuple2 = ["a", 1]
tuple2 = ["a", 1, true]
//剩余参数
let tuple3: [string, number, ...boolean[]]
tuple3 = ["a", 1, true, false]

六、enum

说明：用于定义一组命名的常量值，提高代码的可读性和可维护性。

1.常量枚举

①数字枚举(有反向映射)

enum Direction1 {
    Up,
    Down,
    Left,
    Right
}

console.log("Direction1 value:", Direction1)
//{
    //"0": "Up",
    //"1": "Down",
    //"2": "Left",
    //"3": "Right",
    //"Up": 0,
    //"Down": 1,
    //"Left": 2,
    //"Right": 3
//}
console.log("Direction1.Up value:", Direction1.Up) //0
console.log("Direction1[0] value:", Direction1[0]) //Up

enum Direction2 {
    Up = 5,
    Down,
    Left,
    Right
}

console.log("Direction2 value:", Direction2)
//{
    //"5": "Up",
    //"6": "Down",
    //"7": "Left",
    //"8": "Right",
    //"Up": 5,
    //"Down": 6,
    //"Left": 7,
    //"Right": 8
//}

console.log("Direction2.Up value:", Direction2.Up) //5
console.log("Direction2[5] value:", Direction2[5]) //Up
console.log("Direction2.Down value:", Direction2.Down) //6

备注：成员值依次递增，默认从0开始，可以指定初始值。

②字符串枚举(无反向映射)

enum Direction3 {
    Up = "up",
    Down = "down",
    Left = "left",
    Right = "right"
}

console.log("Direction3 value:", Direction3)
//{
    //"Up": "up",
    //"Down": "down",
    //"Left": "left",
    //"Right": "right"
//}

console.log("Direction3.Up value:", Direction3.Up) //up
console.log("Direction3.Up==up result:", Direction3.Up == "up") //true

2.计算成员

//计算成员
enum Direction4 {
    A = "A".charCodeAt(0),
    B = "B".charCodeAt(0)
}

console.log("Direction4 value:", Direction4)

//{
    //"65": "A",
    //"66": "B",
    //"A": 65,
    //"B": 66
//}

3.常量枚举（减少编译后代码量 无法使用计算成员）

①不使用常量枚举编译前后

//编译前
enum Direction5 {
    Up,
    Down,
    Left,
    Right
}

const direction1 = Direction5.Up

//编译后
var Direction5;
(function (Direction5) {
    Direction5[Direction5["Up"] = 0] = "Up";
    Direction5[Direction5["Down"] = 1] = "Down";
    Direction5[Direction5["Left"] = 2] = "Left";
    Direction5[Direction5["Right"] = 3] = "Right";
})(Direction5 || (Direction5 = {}));
const direction1 = Direction5.Up;

②使用了常量枚举编译前后

//编译前
const enum Direction6 {
    Up,
    Down,
    Left,
    Right
}

const direction2 = Direction6.Up

//编译后
const direction2 = 0 /* Direction6.Up */;

七、type

1.类型别名

type User = {
    name: string,
    age: number
}
let user1: User = {
    name: "张三",
    age: 20
}
type customFunction = () => void
const customFunction1: customFunction = () => "test";

备注：使用类型进行函数类型限制时，返回值为void时，并未严格按照返回值为void限制。

2.联合类型

type StringOrNumber = string | number
let stringOrNumber1:StringOrNumber = "YES"

type Gender = '男' | '女'
let gender1:Gender = '男'

3.交叉类型

type School = {
    schoolName: string
}
type Grade = {
    gradeName: string
}
type Class = {
    className: string
}
type Student = School & Grade & Class

let student1: Student = {
    schoolName: "学校",
    gradeName: "年级",
    className: "班级"
}

八、类型声明文件

说明：用于为已有的JavaScript库或模块提供类型信息，使TypeScript编译器在使用时进行类型检查（以.d.ts为后缀）。

1.test.js

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

2.test.d.ts

declare function sum(a: number, b: number): number;

export {sum};

3.index.ts

import {sum} from "./test.js";
//const totalSum = sum("a", 2); //TS2345: Argument of type string is not assignable to parameter of type number
const totalSum = sum(1, 2); //totalSum 类型为 number

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