为什么我的控制台是说NaN是类扩展Javascript

Question

所以我做了一个项目，当我试图从类的父类获取参数时，它说是NaN，而另一个是true。在这里，代码：

​

class transportasi {//class parent
  constructor(nama,roda,pintu){
  this.nama = nama
  this.roda = roda
  this.pintu = pintu

  }
}

class mobil extends transportasi{//Class Children
  constructor(roda,lampu){
    super(roda)//the problem
    this.lampu = lampu
  }

  jmlahfeature(){
    return this.lampu + this.roda 
  }
}
const mobil1 = new mobil(2,4)//the problem

//I cant fill the value of roda only lampu
console.log("Hasil Perhitungan Feature mobil : " + mobil1.jmlahfeature())

​

我想要它，这样我就可以填充参数roda的值。所以它没有在控制台中说NaN。

Answer 1

正如伊瓦尔所指出的，roda是第二个参数，并且您只传递了超级()中的第一个参数。

下面的代码应该给出您想要的结果。

class transportasi {//class parent
    constructor(nama,roda,pintu){
    this.nama = nama
    this.roda = roda
    this.pintu = pintu
    
    }
}

class mobil extends transportasi{//Class Children
    constructor(roda,lampu){
        super('here should be some value', roda) 
        this.lampu = lampu
    }
    
    jmlahfeature(){
        return this.lampu + this.roda 
    }
}
const mobil1 = new mobil(2,4)//the problem

//I cant fill the value of roda only lampu
console.log("Hasil Perhitungan Feature mobil : " + mobil1.jmlahfeature())

Answer 2

您没有为this.roda = roda分配任何值，您可以尝试使用此方法。

class transportasi {//class parent
    constructor(nama,roda,pintu){
    this.nama = nama
    this.roda = roda
    this.pintu = pintu
  
    }
  }
  
  class mobil extends transportasi{//Class Children
    constructor(roda,lampu){
      super(roda)//the problem
      this.roda = roda
      this.lampu = lampu
    }
  
    jmlahfeature(){
      return this.lampu + this.roda 
    }
  }
  const mobil1 = new mobil(2,4)//the problem
  
  //I cant fill the value of roda only lampu
  console.log("Hasil Perhitungan Feature mobil : " + mobil1.jmlahfeature())

Answer 3

而不是为父类和子类提供单个参数，而是提供一个具有命名属性的对象。如果未将所需的属性分配给父参数，则子类中的简单测试可以分配默认值。

​

class transportasi {
  constructor(args = {}) {
    args = Object.assign({
      nama: false,
      roda: false,
      pintu: false
    }, args);

    this.nama = args.nama;
    this.roda = args.roda;
    this.pintu = args.pintu;
  }
}

class mobil extends transportasi {
  constructor(args = {}) {
    super(args)
    this.lampu = args.lampu || 0;
  }
  jmlahfeature() {
    return this.lampu + this.roda
  }
}


/* correctly named property - Maths should succeed */
const args = {
  lampu: 2,
  roda: 4
};
const app1 = new mobil(args);
console.log(app1.jmlahfeature());

/* incorrectly named, default value of zero used */
const bogus = {
  xlamxpu: 23,
  roda: 33
}
const app2 = new mobil(bogus);
console.log(app2.jmlahfeature());

​