ES6 Class通过mixins进行多重继承

Question

我试图使用mixins来理解ES6多重继承。

我关注this article（简单的mixins）。但是当我运行代码时，我的输出是：

1. main
2. Uncaught ReferenceError: this is not defined，
   并且错误再次指向console.log('main')

我在最新版本的Chrome上运行它。这是我的代码：

const RaceDayService = superclass => class extends superclass { 
    constructor(){
        console.log('service');
    }
}

const RaceDayDB = superclass => class extends superclass { 
    constructor(){
        console.log('db');
    }
}

class RaceDayUI {
    constructor(){
        console.log('ui');
    }
}

class RaceDay extends RaceDayDB(RaceDayService(RaceDayUI)){
    constructor(options){
        console.log('main');
    }
}

const raceDay = new RaceDay();

关于我做错的任何想法？

谢谢！

Answer 1

如果您的超类包含构造函数，则必须在子构造函数中调用super()方法：

const RaceDayService = superclass => class extends superclass { 
    constructor(){
        super();
        console.log('service');
    }
}

const RaceDayDB = superclass => class extends superclass { 
    constructor(){
        super();
        console.log('db');
    }
}

class RaceDayUI {
    constructor(){
        console.log('ui');
    }
}

class RaceDay extends RaceDayDB(RaceDayService(RaceDayUI)){
    constructor(options){
        super();
        console.log('main');
    }
}

const raceDay = new RaceDay();