本系列目的: 列出TypeScript與JavaScript的不同點, 縮小文件內容, 提高學習速度. 原文件地址: https://www.tslang.cn/index.html

類

簡單使用

在TypeScript裡，成員都預設為 public, 成員可以額被標記 private, protected, 或者static

// --------------------- public
class Animal {
    name: string;
    constructor(theName: string) { this.name = theName; }
    move
 
(distanceInMeters: number = 0) {
        console.log(`${this.name} moved ${distanceInMeters}m.`);
    }
}



// --------------------- public 同上
class Animal {
    public name: string;
    public constructor(theName: string) { this.name = theName; }
    public move(distanceInMeters: number) {
        console.
 
log(`${this.name} moved ${distanceInMeters}m.`);
    }
}



// --------------------- private
class Animal {
    private name: string;
    constructor(theName: string) { this.name = theName; }
}

new Animal("Cat").name; // 錯誤: 'name' 是私有的.



// --------------------- protected
class Person {
    protected name:
 
 string;
    constructor(name: string) { this.name = name; }
}

class Employee extends Person {
    private department: string;

    constructor(name: string, department: string) {
        super(name)
        this.department = department;
    }

    public getElevatorPitch() {
        return `Hello, my name is ${this.name} and I work in ${this.department}.`;
    }
}

let howard = new Employee("Howard", "Sales");
console.log(howard.getElevatorPitch());
console.log(howard.name); // 錯誤



// --------------------- 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}));

readonly修飾符

你可以使用 readonly關鍵字將屬性設定為只讀的, 只讀屬性必須在宣告時或建構函式裡被初始化.

class Octopus {
    readonly name: string;
    readonly numberOfLegs: number = 8;
    constructor (theName: string) {
        this.name = theName;
    }
}
let dad = new Octopus("Man with the 8 strong legs");
dad.name = "Man with the 3-piece suit"; // 錯誤! name 是隻讀的.


// --------------------------- 也可以省略成這樣

class Octopus {
    readonly numberOfLegs: number = 8;
    constructor(readonly name: string) {
    }
}

存取器

這個在es2015也有, 複習一下.
注意在編譯的時候要用tsc -t es5命令輸出es5, tsc命令會報錯

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);
}

抽象類

抽象類做為其它派生類的基類使用。 它們一般不會直接被例項化。 不同於介面，抽象類可以包含成員的實現細節。 abstract關鍵字是用於定義抽象類和在抽象類內部定義抽象方法。(此處類似java)

abstract class Animal {
    abstract makeSound(): void;
    move(): void {
        console.log('roaming the earch...');
    }
}



// 如果Animal作為型別去用的話, 不可以使用抽象類裡沒有的屬性
abstract class Department {

    constructor(public name: string) {
    }

    printName(): void {
        console.log('Department name: ' + this.name);
    }

    abstract printMeeting(): void; // 必須在派生類中實現
}

class AccountingDepartment extends Department {

    constructor() {
        super('Accounting and Auditing'); // 在派生類的建構函式中必須呼叫 super()
    }

    printMeeting(): void {
        console.log('The Accounting Department meets each Monday at 10am.');
    }

    generateReports(): void {
        console.log('Generating accounting reports...');
    }
}

let department: Department; // 允許建立一個對抽象型別的引用
department = new Department(); // 錯誤: 不能建立一個抽象類的例項
department = new AccountingDepartment(); // 允許對一個抽象子類進行例項化和賦值
department.printName();
department.printMeeting();
department.generateReports(); // 錯誤: 方法在宣告的抽象類中不存在

把類當初介面

與java語言不同的是, ts介面可以繼承類.
類定義會建立兩個東西：類的例項型別和一個建構函式。 因為類可以創建出型別，所以你能夠在允許使用介面的地方使用類. 即使類裡面可以實現方法, 但在interface繼承了之後下面這個例子中的point3d變數還需要自己再實現一次.

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

interface Point3d extends Point {
    z: number;
}

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



// ---------------------------

class Point {
    x: number;
    y: number;
    public gkd() : string {
        return 'aasd';
    };
}

interface Point3d extends Point {
    z: number;
}

let point3d: Point3d = { x: 1, y: 2, z: 3, gkd: ():string => {
    return '123';
} };