抽象類

abstract class Machine {
    constructor(public manufacturer: string) {
    }

    // An abstract class can define methods of it's own, or...
    summary(): string {
        return `${this.manufacturer} makes this machine.`;
    }
    
    // Require inheriting classes to implement methods
    abstract moreInfo(): string;
}

class Car extends Machine {
    constructor(manufacturer: string, public position: number, protected speed: number) {
        super(manufacturer);
    }
    
    move() {
        this.position += this.speed;
    }
    
    moreInfo() {
        return `This is a car located at ${this.position} and going ${this.speed}mph!`;
    }
}

let myCar = new Car("Konda", 10, 70);
myCar.move(); // position is now 80
console.log(myCar.summary()); // prints "Konda makes this machine."
console.log(myCar.moreInfo()); // prints "This is a car located at 80 and going 70mph!"

抽象類是其他類可以擴充套件的基類。他們不能自己例項化（即你不能做 new Machine("Konda")）。

Typescript 中抽象類的兩個關鍵特徵是：

1. 他們可以實現自己的方法。
2. 他們可以定義繼承類必須實現的方法。

因此，抽象類在概念上可以被視為介面和類的組合。