demo

使用ts完成一个todomvc的demo

核心概念

接口

参数校验

interface LabelledValue {
  label: string;
}

function printLabel(labelledObj: LabelledValue) {
  console.log(labelledObj.label);
}

let myObj = {size: 10, label: "Size 10 Object"};
printLabel(myObj);

接口可以用来校验参数的类型，参数是否存在等等。

属性预定义

interface SquareConfig {
    color?: string;
    width?: number;
  }
  
function createSquare(config: SquareConfig): { color: string; area: number } {
    let newSquare = {color: "white", area: 100};
    if (config.clor) {
      // Error: Property 'clor' does not exist on type 'SquareConfig'
      newSquare.color = config.clor;
    }
    if (config.width) {
      newSquare.area = config.width * config.width;
    }
    return newSquare;
}
  
let mySquare = createSquare({color: "black"});

属性只读

interface Point {
    readonly x: number;
    readonly y: number;
} 

let p1: Point = { x: 10, y: 20 };
p1.x = 5; // error!

注意事项

对象字面量形式会被特殊对待而且会经过额外属性检查

interface SquareConfig {
    color?: string;
    width?: number;
}

function createSquare(config: SquareConfig): { color: string; area: number } {
    let newSquare = { color: "white", area: 100 };
    if (config.clor) {
        // Error: Property 'clor' does not exist on type 'SquareConfig'
        newSquare.color = config.clor;
    }
    if (config.width) {
        newSquare.area = config.width * config.width;
    }
    return newSquare;
}

let mySquare = createSquare({ color: "black" });

createSquare({ colour: "red", width: 100 }); 
// Error: Property 'colour does no exist on type 'SquareConfig'

如果想解决这个问题有三种解决办法

// 1. 将对象字面量复制给变量，传入变量不会被进行额外属性检查
let skipLiteral = { colour: "red", width: 100 };
createSquare(skipLiteral);

// 2.采用类型断言，使用as操作符，告诉编译器我传入的参数对象就是你要的类型
createSquare({ colour: "red", width: 100 } as SquareConfig);

// 3.第三种方式，添加万能校验符，这个符号会包容color、width之外所有其他属性，慎用
interface SquareConfig {
    color?: string;
    width?: number;
    [propName: string]: any;
}

函数类型

interface SearchFunc {
  (source: string, subString: string): boolean;
}

可索引的类型

interface StringArray {
  [index: number]: string;
}

let myArray: StringArray;
myArray = ["Bob", "Fred"];

let myStr: string = myArray[0];

ts支持两种索引签名，字符串和数值，同时使用的时候，数值索引返回的类型必须是字符串索引返回类型的子类，因为js解析的时候会将数值索引转换为字符串索引，所以数值索引返回的类型必须与字符串返回的类型保持一致（或子类）。

class Animal {
    name: string;
}
class Dog extends Animal {
    breed: string;
}

// 错误：使用数值型的字符串索引，有时会得到完全不同的Animal!
interface NotOkay {
    [x: number]: Animal;
    [x: string]: Dog;
}

类类型

与C#或Java里接口的基本作用一样，TypeScript也能够用它来明确的强制一个类去符合某种契约。

interface ClockInterface {
    currentTime: Date;
}

class Clock implements ClockInterface {
    currentTime: Date;
    constructor(h: number, m: number) { }
}

接口继承

interface Shape {
    color: string;
}

interface Square extends Shape {
    sideLength: number;
}

类

继承 extends

class Animal {
    move(distanceInMeters: number = 0) {
        console.log(`Animal moved ${distanceInMeters}m.`);
    }
}

class Dog extends Animal {
    bark() {
        console.log('Woof! Woof!');
    }
}

const dog = new Dog();
dog.bark();
dog.move(10);
dog.bark();

存取器

let passcode = "secret passcode";

class Employee {
    private _fullName: string;

    get fullName(): string {
        return this._fullName;
    }

    set fullName(newName: string) {
        if (passcode && passcode == "secret passcode") {
            this._fullName = newName;
        }
        else {
            console.log("Error: Unauthorized update of employee!");
        }
    }
}

let employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
    alert(employee.fullName);
}

静态属性 static

class Grid {
    static origin = {x: 0, y: 0};
    calculateDistanceFromOrigin(point: {x: number; y: number;}) {
        let xDist = (point.x - Grid.origin.x);
        let yDist = (point.y - Grid.origin.y);
        return Math.sqrt(xDist * xDist + yDist * yDist) / this.scale;
    }
    constructor (public scale: number) { }
}

let grid1 = new Grid(1.0);  // 1x scale
let grid2 = new Grid(5.0);  // 5x scale

console.log(grid1.calculateDistanceFromOrigin({x: 10, y: 10}));
console.log(grid2.calculateDistanceFromOrigin({x: 10, y: 10}));

把类当做接口使用

class Point {
    x: number;
    y: number;
}

interface Point3d extends Point {
    z: number;
}

let point3d: Point3d = {x: 1, y: 2, z: 3};

函数

let myAdd: (x: number, y: number) => number =
    function(x: number, y: number): number { return x + y; };

重载

方法是为同一个函数提供多个函数类型定义来进行函数重载。 编译器会根据这个列表去处理函数的调用。

let suits = ["hearts", "spades", "clubs", "diamonds"];

function pickCard(x: {suit: string; card: number; }[]): number;
function pickCard(x: number): {suit: string; card: number; };
function pickCard(x): any {
    // Check to see if we're working with an object/array
    // if so, they gave us the deck and we'll pick the card
    if (typeof x == "object") {
        let pickedCard = Math.floor(Math.random() * x.length);
        return pickedCard;
    }
    // Otherwise just let them pick the card
    else if (typeof x == "number") {
        let pickedSuit = Math.floor(x / 13);
        return { suit: suits[pickedSuit], card: x % 13 };
    }
}

let myDeck = [{ suit: "diamonds", card: 2 }, { suit: "spades", card: 10 }, { suit: "hearts", card: 4 }];
let pickedCard1 = myDeck[pickCard(myDeck)];
alert("card: " + pickedCard1.card + " of " + pickedCard1.suit);

let pickedCard2 = pickCard(15);
alert("card: " + pickedCard2.card + " of " + pickedCard2.suit);

泛型

泛型接口

function identity<T>(arg: T): T {
    return arg;
}

使用尖括号传入泛型变量，它会根据参会类型智能赋值。比如arg是number，那么T就会被赋值为number。

泛型类

class GenericNumber<T> {
    zeroValue: T;
    add: (x: T, y: T) => T;
}

let myGenericNumber = new GenericNumber<number>();
myGenericNumber.zeroValue = 0;
myGenericNumber.add = function(x, y) { return x + y; };

在这里，泛型作为一种变量，可供用户调用的时候动态约束类属性。

在泛型约束中使用类型参数

function getProperty(obj: T, key: K) {
    return obj[key];
}

let x = { a: 1, b: 2, c: 3, d: 4 };

getProperty(x, "a"); // okay
getProperty(x, "m"); // error: Argument of type 'm' isn't assignable to 'a' | 'b' | 'c' | 'd'.