TS学习之类

定义类

class Person {
    name: string;   //属性
    constructor(_name: string) {
        this.name = _name;
    }   //构造函数
    sayHello(): string {
        return "Hi,everyone"
    }   //方法
}

let firstOne = new Person("Fred")   //实例化类

继承：继承使用关键字extends，调用父类使用super，子类继承父类的属性和方法，并且子类可以改写父类的属性和方法

class Animal {
    name: string;
    constructor(_name: string) {
        this.name = _name;
    }
    skinColour(color: string = "black"): void {
        console.log(`${this.name} skin colour is ${color}`)
    }
}

class Horse extends Animal {
    constructor(name: string) { super(name) }
    skinColour(color: string = "brown"): void {
        console.log(`I'am ${this.name}`);
        super.skinColour("brown");
    }
}

let horse = new Horse("horse");
horse.skinColour()
// I'am horse
// horse skin colour is brown

public、private、protected、readonly

• public（不声明默认都为public，也可以显示的设置为public）

class Person {
    public name: string;   //属性
    public constructor(_name: string) {
        this.name = _name;
    }   //构造函数
    public sayHello(): string {
        return "Hi,everyone"
    }   //方法
}

let firstOne = new Person("Fred")   //实例化类

• private（private的成员不能被外部访问；比较带有private或protected成员的类型时，两个类型兼容的条件是private或protected的成员必须相同切来至同一个声明（同一个类））

class Person {
    private name: string;   
    public constructor(_name: string) {
        this.name = _name;
    }   
}

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

let firstOne = new Person("Fred")
console.log(firstOne.name)  //error: Property 'name' is private;
let lastOne = new Employee("Fred")
firstOne = lastOne  // error: Type 'Employee' is not assignable to type 'Person'.Types have separate declarations of a private property 'name'.

• protected（protected和private相似，但protected成员可以在派生类中访问（能被继承，但不能在实例中访问，若构造函数是protected，则不能被实例化，只能被继承））

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

class Employee extends Person {
    private department: string;   
    public constructor(name: string,department:string) {
        super(name);
        this.department = department;
    }   
}

let Bob = new Person;   //error: Constructor of class 'Person' is protected
let fred = new Employee("fred","test");
console.log(fred.name)  //error: Property 'name' is protected

• readonly（设置属性为只读，必须在声明时或构造函数里初始化）

class Person {
    readonly name: string;   
    constructor(_name: string) {
        this.name = _name;
    }   
}

let fred = new Person("fred");
fred.name = "Bob"   //error: Cannot assign to 'name' because it is a constant or a read-only property.

参数属性（参数属性通过给构造函数参数添加一个访问限定符来声明（public,private,protected）,把声明和赋值合并至一处）

class Person {
    constructor(private name: string) { }
    sayHello(): void {
        console.log(`my name is ${this.name}`)
    }
}

let fred = new Person("fred");
fred.sayHello() //my name is fred

存取器（get、set   只带有 get不带有set的存取器自动被推断为readonly）

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) {
    console.log(employee.fullName);
}

静态属性（static，不能被实例访问，在类里面访问时，需要加上类名）

class Person {
    static height:number = 180;
    constructor(private name: string) { }
    sayHello(): void {
        console.log(`my name is ${this.name}, I height is ${Person.height}`)
    }
}

let fred = new Person("fred");
fred.sayHello() //my name is fred, I height is 180

抽象类（abstract，抽象类做为其它派生类的基类使用。 它们一般不会直接被实例化。抽象类中的抽象方法不包含具体实现并且必须在派生类中实现）

abstract class Person {
    constructor(public name: string) { }
    abstract sayHello():void;
}

class Empoloy extends Person{
    constructor(){
        super("Fred")
    }
    sayHello(){
        console.log(`my name is ${this.name}`)
    }
}

let firstOne = new Empoloy();
firstOne.sayHello();    //my name is Fred