TypeScript前端学习（四）

前言

        还是分享的笔记，大佬请绕行！

---

一、类的定义和继承

console.log("----对象---");
var people = {
    "name": "张三",
    syaHi() {
        console.log("HI,my name is " + this.name);
    }
}
people.syaHi();

console.log("----类---");
class People {
    name: string;

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

    syaHi() {
        console.log("HI,my name is " + this.name);
    }
}

//实例化类
var people2 = new People("李四");
people2.syaHi();

console.log("----类的继承---");
//类的继承
class Student extends People {
    constructor(name: string) {
        super(name);
    }

    syaHi() {
        console.log("HI,my name is " + this.name);
    }

    makeWorks() {
        console.log("我在做作业");
    }
}

var student = new Student("小明");
student.syaHi() + "," + student.makeWorks();

class Teacher extends People {
    subject: string;

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

    syaHi() {
        super.syaHi();
        console.log("同学们好");
    }

    teach() {
        console.log(this.name + ",我在教" + this.subject);
    }
}

var teacher = new Teacher("李老师", "数学");
teacher.syaHi();
console.log("----------")
teacher.teach();

示例效果

二、类的访问权限

console.log("----类的访问权限---");
class Animal {
    //private className:string="Animal";  //私有属性，只能在类内部访问（继承他的类用就会报错了）
    className: string = "Animal";

    protected constructor() {
        this.className = "Animal";    //受保护的构造函数，只能在类内部访问（继承他的类用就会报错了）
    }
}
//var animal = new Animal();  //TS2674: Constructor of class Animal is protected and only accessible within the class declaration.

class Dog extends Animal {
    name: string;

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

    run() {
        console.log(this.name + "在跑");
    }
}
var dog = new Dog("小狗");
dog.run();

示例运行效果
注释的语句，报错描述写在注释里了
报错就是因为设置了protected等关键字

三、只读属性与存取器

console.log("----只读属性---")

//
class Circle {
    readonly PI: number = 3.14;
    readonly r: number;

    constructor(r: number) {
        this.r = r;
    }

    getArea() {
        return this.PI * this.r * this.r;
    }
}
var circle = new Circle(10);
console.log(circle.getArea());

//circle.r = 20; //TS2540: Cannot assign to 'r' because it is a read-only property.

console.log("----存取器---");
class Circle2 {
    readonly PI: number = 3.14;
    protected r: number = 0;
    set R(r: number) {
        if (r < 0) {
            return;
        }
        this.r = r;
    }
    get R(): number {
        return this.r;
    }
    getArea() {
        return this.PI * this.r * this.r;
    }
}
var circle2 = new Circle2();
circle2.R = 10;
console.log(circle2.R);
console.log(circle2.getArea());

示例运行效果

---

总结

• 看起来跟其他面向对象的后端语言真像
• 这次没有用tsc命令生成js对比，有兴趣的可以自己生成对比看看
  纯粹的笔记备忘，uping！