javascript - Typescript 中的编译错误

Question

我是 Typescript 新手。

我今天编写了下面的代码，但在编辑器中出现了编译错误。

Type 'EngineFactory' is not assignable to type 'EngineInterface'. Property 'run' is missing in type 'EngineFactory'.

我明白此错误消息的含义，但我不知道如何修复此错误。请教我修复此错误的适当方法。

interface EngineInterface {

    run();

}


class HondaEngine implements EngineInterface{

    constructor() {}

    run() {}

}


class ToyotaEngine implements EngineInterface{

    constructor() {}

    run() {}

}

enum EngineType {

    Honda,
    Toyota

}


class EngineFactory {

    constructor(engineType: EngineType){

        if (engineType === EngineType.Honda) {
            return new HondaEngine();
        }

        if (engineType === EngineType.Toyota) {
            return new ToyotaEngine();
        }

    }

}



class Car {

    private engine: EngineInterface;

    constructor(engineType: EngineType) {
        this.engine = new EngineFactory(engineType);
    }

}



let car = new Car(EngineType.Toyota);

注意

按照下面的方式编写代码不会产生编译错误。但我想知道是否有另一种方法可以修复我上面粘贴的错误。

class EngineFactory {

    constructor(){}

    static getEngine(engineType: EngineType): EngineInterface {

        if (engineType === EngineType.Honda) {
            return new HondaEngine();
        }

        if (engineType === EngineType.Toyota) {
            return new ToyotaEngine();
        }
    }
}

class Car {

    private engine: EngineInterface;

    constructor(engineType: EngineType) {
        this.engine = EngineFactory.getEngine(engineType);
    }

}


let car = new Car(EngineType.Toyota);

我希望我可以在构造函数方法中定义返回类型...

class EngineFactory {

    // Typescript won't let me define returned type in constructor.
    constructor(engineType: EngineType): EngineInterface{

        if (engineType === EngineType.Honda) {
            return new HondaEngine();
        }

        if (engineType === EngineType.Toyota) {
            return new ToyotaEngine();
        }

    }

}

Answer 1

1. 在构造函数中返回对象是没有意义的。

2. 这样写代码会更清晰:

   类引擎工厂{ 构造函数(){}

   static getEngine(engineType: EngineType): EngineInterface {
        switch(EngineType):
              //case  ....
   }
   

   }