如何设置属于基类[继承]的子类对象的属性（属性）？ （将Base的attr传递给Child）

Question

I am new to classes and OOP and was following a tutorial explaining classes and inheritance and stumbled upon something.

How can I pass the values that belong to Base class' constructor into the child class?

For example if a BASE class has

this.name=name
this .age=age

and the child class inherits Base class

In Base class,there are two properties

this.childSchoool=school
this.childfiends=friends

I can access the functions of Base Class using super().func;

if I make a child class object like

let childobj = new child("school_name", 6);

It'll initialise the child object with schoolname and age but

HOW can I set name and age of the child class object?

Answer 1

you have to provide method to do so:

 class Animal { constructor(name) { this.name = name; } setName = (name) => this.name = name; } class Cat extends Animal { constructor(name) { super(name); } } const myCat = new Cat('Tom'); console.log(myCat.name); // Logs 'Tom' myCat.setName('Silvester'); console.log(myCat.name); // Logs 'Silvester' 

Answer 2

How can I pass the values that belong to Base class' constructor into the child class?

You do it through super() which calls the Base class constructor to initialise the properties inherited from the Base class.

 class Base{ constructor(name, age){ this._name = name; this._age = age; } } class Child extends Base{ constructor(name, age, schoolname){ super(name, age); //initializes the _name & _age properties this.schoolname = schoolname; } get name(){ return this._name; } set name(name){ this._name = name; } get age(){ return this._age; } set age(age){ this._age = age; } //getter setter for schoolname } const child = new Child("foo", 42, "bar"); console.log(child.name); console.log(child.age); child.name = "baz" console.log(child.name); 

In the above code the super(name, age) call in the Child class calls the constructor(name, age) of the Base class.

Now in the constructor the this._name & this._age is set, but the this here is actually the object of the Child class.

When you invoke the new Child("foo", 42, "bar") a new object is created, then the this is assigned to the new object. In the super(name, age) call the parameters name and age are used to initialise the this object so that the child instance will have the _name and _age properties from the Base class initialised with these values.

Answer 3

Quite simply, if you have a class (classB) that is inheriting from another (classA), in the classB constructor you will take in parameters for the classA constructor and pass them along.

MDN explains this.

class Base {
  constructor(name, age){
    this.name = name;
    this.age = age;
  }
}

class Child extends Base {
  constructor(name, age, school, friends){
    super(name, age); //pass along to the Base constructor
    this.school = school;
    this.friends = friends;
  }
}

let achild = new Child('ben', 4, 'School1', 99);

Parameter order matters. However, you can also use named parameters:

let bchild = new Child(school='school2', age=9, name='chris', friends=22);

Or you can use spread syntax to pass in a map or object:

let amap = new Map([['name', 'sally'],['school', 'school1'],['age', 10],['friends', 9001]]);

let cchild = new Child(...amap);