<笔记>typescript-类

1. 类的继承和基本类型指定

ts中super必须被调用，否则会提示

Constructors for derived classes must contain a 'super' call

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

class Horse extends Animal {
    constructor(name: string) { super(name); } // 1.相当于super.call(this, props)
    move(distanceInMeters = 45) {
        console.log("Galloping...");        
        // 2. 相当于super.prototype.move.call(this, distanceInMeters)         super.move(distanceInMeters);
    }
}
let tom: Animal = new Horse("Tommy the Palomino");
tom.move(34);

2. 修饰符（公共/私有/受保护）

1. 公共-public

上面的类本质上为：

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

2. 私有-private

class Animal {  private name: string;  constructor(theName: string) { this.name = theName; }}new Animal("Cat").name; // 错误: 'name' 是私有的.

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

class Rhino extends Animal {
    constructor() { super("Rhino"); }
}

class Employee {
    private name: string;
    constructor(theName: string) { this.name = theName; }
}

let animal = new Animal("Goat");
let rhino = new Rhino();
let employee = new Employee("Bob");

animal = rhino; // 正确。两者共享private成员
animal = employee; // 错误: Animal 与 Employee 不兼容. 

3. 受保护-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() { // 可以在子类中访问
        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); // 错误；只能在声明类和子类中访问

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

// Employee 能够继承 Person
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");
let john = new Person("John"); // 错误: 'Person' 的构造函数是被保护的.

3. readonly修饰符

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"; // 错误! name 是只读的.

构造函数的参数属性

class Octopus { // 和上面的代码等价
  readonly numberOfLegs: number = 8;
  constructor (readonly name: string) {
  }
}

4. 存取器(get/set)

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);
}

5. 静态属性static

直接通过类访问

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}));

6. 抽象类-abstract

abstract作用：

1. 定义抽象类(抽象类不能被实例化)
2. 定义抽象类内部的抽象方法（不包含具体实现并且必须在派生类中实现）

abstract应用：

abstract class Animal { // 抽象类 
 abstract makeSound(): void; // 抽象方法不包含具体实现 
 move(): void { // 非抽象方法可以包含具体实现    
    console.log('roaming the earch...');  
}}

示例：

abstract class Department {  
    constructor(public name: string) {  
    }  
    printName(): void {   
        console.log('Department name: ' + this.name);  
    }  
    abstract printMeeting(): void;
}
class AccountingDepartment extends Department {  
        constructor() {    
            super("Accounting and Auditing");  
        }  
        printMeeting(): void {    
            console.log('The Accounting Department meets each Monday at 10am.');  
        }  
        generateReports(): void {    
            console.log('Generating accounting reports...');  
        }
}
let department: Department; // 定义变量的类型
department = new Department(); //  ❌不能被实例话
department = new AccountingDepartment();
department.printMeeting();
department.printName();
department.generateReports(); // ❌方法声明在抽象类中不存在

6. 高级技巧-构造函数

在ts中声明类的时候，同时声明了实例类型和构造函数。

class Greeter {
    greeting: string;
    constructor(message: string) {
        this.greeting = message;
    }
    greet() {
        return "Hello, " + this.greeting;
    }
}

let greeter: Greeter;
greeter = new Greeter("world");
console.log(greeter.greet());

其编译成javascript的结果如下：

var Greeter = (function() {  
    function Greeter(message) {    
        this.greeting = message;  
    }  
    Greeter.prototype.greet = function() {    
        return "Hello, " + this.greeting; 
    }  
    return Greeter
}());
var greeter;
greeter = new Greeter("world");
console.log(greeter.greet());