emmm...直接通過測試來看父子關系吧：

class A{
    constructor(){//並非必須
        this.name="class_A";
        //console.log(this) //A {name: "class_A"} (另起一行)B {name: "class_A"} //父類子類分別執行了一次
    }
    static staticCallNameA(){
    return "name_A";
    }
    callNameA(){
    return "name_A";
    }
    static cover(){
    return
 
 "cover_A"
    }
}

class B extends A{
    constructor(){//子類可以不加
    super();//子類必須有
    //console.log(this)//B {name: "class_A"} //會直接打印
    }
    static staticCallNameB(){
    return "nameB";
    }
    callNameB(){
    return "name_B";
    }
    static cover(){
    return "cover_B"
    }
}

console.log(A.name,B.name) //
 
A B //(類名)
console.log(A.staticCallNameA(),B.staticCallNameA()) //static子類繼承父類
console.log(A.cover(),B.cover()) //cover_A cover_B //先讀子類再讀父類
console.log(A.staticCallNameB) //undefined //父類不具備子類特有函數
console.log(A.callNameA,B.callNameA) //undefined undefined //非static方法類不能直接調用

let a=new A(),b=new B; //加不加括號效果一樣
console.log(a.name); //
 
class_A
console.log(a.name,b.name) //class_A class_A
console.log(a.callNameA(),a.callNameB,b.callNameB(),b.callNameA()) //name_A undefined name_B name_A //說明繼承關系同上

歡迎各位大神指點...

JS__class 入坑 chrome測試class 父子類 繼承關系