<2> 继承父原型存在的问题

function Parent(name){ name = "Parent" }
// 给parent的原型加上一个方法
Parent.prototype.parentMethod = function parentMethod(){};
function Child(name ){ name = "child" } 
Child.prototype = Object.create(Parent.prototype);
console.log(
    "constructor:"+ Child.constructor +
    "prototype constructor:"+Child.prototype.constructor
)
Child.prototype.constructor = Child ;//return 
console.log(
    "显示指定自身构造函数之后:\n"+
    "constructor:"+ Child.constructor +
    "prototype constructor:"+Child.prototype.constructor
)
let

打印结果:
在显示指定自身构造函数之后Child.constructor 没有改变
而Child.prototype.constructor 从parent变成child的

chenyanlongdeMacBook-Pro-3:Object chenyanlong$ node inherit_constructor.js 
constructor:function Function() { [native code] }prototype constructor:function Parent(name){ name = "Parent" }
显示指定自身构造函数之后:
constructor:function Function() { [native code] }prototype constructor:function Child(name ){ name = "child" }

2.显示指定原型构造函数为child之后,可以继续使用parent原型有的方法

代码

function Parent(name){ name = "Parent" }
// 给parent的原型加上一个方法
Parent.prototype.parentMethod = function parentMethod(){
    console.log("I am parent method")
};
function Child(name ){ name = "child" } 
Child.prototype = Object.create(Parent.prototype);
console.log(
    "constructor:"+ Child.constructor +
    "prototype constructor:"+Child.prototype.constructor
)
Child.prototype.constructor = Child ;//return 
console.log(
    "显示指定自身构造函数之后:\n"+
    "constructor:"+ Child.constructor +
    "prototype constructor:"+Child.prototype.constructor
)
let  child = new Child()
child.parentMethod()
chenyanlongdeMacBook-P

结果:
child调用parentMethod —> 成功执行了parent的parentMethod

constructor:function Function() { [native code] }prototype constructor:function Parent(name){ name = "Parent" }
显示指定自身构造函数之后:
constructor:function Function() { [native code] }prototype constructor:function Child(name ){ name = "child" }
I am parent method

3.child可以重写parent.prototype的方法

function Parent(name){ name = "Parent" }
// 给parent的原型加上一个方法
Parent.prototype.parentMethod = function parentMethod(){
    console.log("I am parent method")
};
function Child(name ){ name = "child" } 
Child.prototype = Object.create(Parent.prototype);
console.log(
    "constructor:"+ Child.constructor +
    "prototype constructor:"+Child.prototype.constructor
)
Child.prototype.parentMethod = function childMethod(){
    console.log("i am child ,I overwrite the parentMethod")
}
Child.prototype.constructor = Child ;//return 
console.log(
    "显示指定自身构造函数之后:\n"+
    "constructor:"+ Child.constructor +
    "prototype constructor:"+Child.prototype.constructor
)
let  child = new Child()
child.parentMethod()

打印结果：

constructor:function Function() { [native code] }prototype constructor:function Parent(name){ name = "Parent" }
显示指定自身构造函数之后:
constructor:function Function() { [native code] }prototype constructor:function Child(name ){ name = "child" }
i am child ,I overwrite the parentMethod

4. prototype.constructor = child的好处

代码1:

function Parent() {};
function CreatedConstructor() {}
CreatedConstructor.prototype = Object.create(Parent.prototype);
CreatedConstructor.prototype.create = function create() {
  return new this.constructor();
}
new CreatedConstructor().create().create(); 
// error undefined is not a function since constructor === Parent
//这里报错的原因是此时CreatedConstructor.prototype.constructor = function Parent() {};
// 并没有create方法

代码2:

function Parent() {};
function CreatedConstructor() {}
CreatedConstructor.prototype = Object.create(Parent.prototype);
CreatedConstructor.prototype.constructor = CreatedConstructor; // set right constructor for further using
CreatedConstructor.prototype.create = function create() {
  return new this.constructor();
}
//这里不会报错的原因是:
//CreatedConstructor.prototype.constructor =  CreatedConstructor
//有自己的create方法
new CreatedConstructor().create().create(); // it's pretty fine

4.1 prototype.constructor = child 时,prototype.constructor 可以调用parent原型的方法吗

结果：可以显示调用

function Parent() {};
Parent.prototype.ParentMethod = function h(){console.log("i am parent.prototype method")}
function CreatedConstructor() {}
CreatedConstructor.prototype = Object.create(Parent.prototype);
CreatedConstructor.prototype.constructor = CreatedConstructor; // set right constructor for further using
CreatedConstructor.prototype.create = function create() {
  return new this.constructor();
}
CreatedConstructor.prototype.childMethod = function (){
    this.constructor.prototype.ParentMethod();
}
new CreatedConstructor().create().create().childMethod(); // it's pretty fine

5. 在child.prototype.method 中调用parent.prototype.method的方法

function ParentWithStatic() {}
ParentWithStatic.prototype.startPosition = { x: 0, y:0 };
ParentWithStatic.prototype.getStartPosition = function getStartPosition() {
  return this.startPosition;
}
function Child(x, y) {
  this.position = {
    x: x,
    y: y
  };
}
Child.prototype = Object.create(ParentWithStatic.prototype)
Child.prototype.constructor = Child;
Child.prototype.constructor = ParentWithStatic;
Child.prototype.getOffsetByInitialPosition = function getOffsetByInitialPosition() {
  var position = this.position;
  var startPosition = this.constructor.prototype.getStartPosition(); // error undefined is not a function, since the constructor is Child
  return {
    offsetX: startPosition.x - position.x,
    offsetY: startPosition.y - position.y
  }
};
child = new Child();