检索原型属性时出现TypeError

在外面调用inheritPrototype怎么样?

这个对我有效:

function inheritPrototype (sup, sub) {
  var proto = Object.create(sup.prototype);
  Object.defineProperty(proto, "constructor", {value : sub});
  sub.prototype = proto;
}
function Person (name, age) {
  this.name = name;
  this.age = age;
  if (!Person.prototype.getName) {
    Person.prototype.getName = function () { return this.name; }
    Person.prototype.getAge = function () { return this.age; }
  }
}
function Employee (name, age, skills) {
  Person.call(this, name, age);
  this.skills = skills;
  if (!Employee.prototype.getSkills) {
    Employee.prototype.getSkills = function () { return this.skills; }
  }
}
inheritPrototype(Person, Employee); // <= FIX
var person = new Person ("Dave", 21);
var employee = new Employee ("David", 22, ["C", "C++", "Java", "Python", "PHP"]);
console.log(person.getName()); // returns "Dave"
console.log(employee.getSkills()); // returns ["C", "C++", "Java", "Python", "PHP"]
console.log(employee.getName());  // returns David

这个问题主要是由于当inheritPrototype方法被调用时原型引用不匹配。

在inheritPrototype方法中，你有object .create(sup.prototype)，它试图从原型中创建一个新实例，该实例与创建Employee对象时使用的对象引用不同。

这可以在为Employee prototype打印的控制台日志中看到，其中为prototype创建了一个新引用，其中不调用inheritPrototype方法的EmployeeOne具有相同的引用。

所以，您看到异常的原因是因为引用不匹配。即使你在引用原型，在调用inheritMethod之前和之后的引用也是不同的。

我没有文档来支持我的理论，但是，我相信在inheritPrototype方法调用的情况下，原型引用已经改变，这就是为什么新添加的方法getSkills在该对象的原型链查找中不可见的情况。

然而，一旦原型值在第一个员工调用期间更新，后续的员工对象就能够看到新的getSkills，因为原型引用现在指向早期调用的原型引用。

function inheritPrototype(sup, sub) {
  var proto = Object.create(sup.prototype);
  Object.defineProperty(proto, "constructor", {
    value: sub
  });
  sub.prototype = proto;
}
function Person(name, age) {
  this.name = name;
  this.age = age;
  if (!Person.prototype.getName) {
    Person.prototype.getName = function () {
      return this.name;
    }
    Person.prototype.getAge = function () {
      return this.age;
    }
  }
}
function Employee(name, age, skills) {
  Person.call(this, name, age);
  this.skills = skills;
  var p = Employee.prototype;
  if (!Employee.prototype.getSkills) {
    inheritPrototype(Person, Employee);
    Employee.prototype.getSkills = function () {
      return this.skills;
    }
  }
  console.log("Employee with inheritPrototype invocation : " + (p === Employee.prototype));
}
function EmployeeOne(name, age, skills) {
  Person.call(this, name, age);
  this.skills = skills;
  var p = EmployeeOne.prototype;
  if (!EmployeeOne.prototype.getSkills) {
    EmployeeOne.prototype.getSkills = function () {
      return this.skills;
    }
  }
  console.log("EmployeeOne without inheritPrototype invocation : " + (p === EmployeeOne.prototype));
}
var person = new Person("Dave", 21);
var employee = new Employee("David", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
var employeeOne = new EmployeeOne("DavidOne", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
var employeeTwo = new Employee("David", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
console.log(employeeTwo.getSkills());

我试图在继承原型方法后查找Employee构造函数的引用，我上面对原型的新引用的解释证明是正确的。

function inheritPrototype(sup, sub) {
  var proto = Object.create(sup.prototype);
  Object.defineProperty(proto, "constructor", {
    value: sub
  });
  sub.prototype = proto;
}
function Person(name, age) {
  this.name = name;
  this.age = age;
  if (!Person.prototype.getName) {
    Person.prototype.getName = function() {
      return this.name;
    }
    Person.prototype.getAge = function() {
      return this.age;
    }
  }
}
function Employee(name, age, skills) {
  Person.call(this, name, age);
  this.skills = skills;
  var p = Employee.prototype;
  if (!Employee.prototype.getSkills) {
    inheritPrototype(Person, Employee);
    Employee.prototype.getSkills = function() {
      return this.skills;
    }
  } else {
    inheritPrototype(Person, Employee);
  }
  if (employeeTwoPrototype !== undefined) {
    console.log("Employee with 2nd inheritPrototype invocation : " + (p === employeeTwoPrototype));
    console.log("Employee with 2nd inheritPrototype invocation : " + (p === Employee.prototype));
  } else {
    console.log("Employee with inheritPrototype invocation : " + (p === Employee.prototype));
  }
}
function EmployeeOne(name, age, skills) {
  Person.call(this, name, age);
  this.skills = skills;
  var p = EmployeeOne.prototype;
  if (!EmployeeOne.prototype.getSkills) {
    EmployeeOne.prototype.getSkills = function() {
      return this.skills;
    }
  }
  console.log("EmployeeOne without inheritPrototype invocation : " + (p === EmployeeOne.prototype));
}
var person = new Person("Dave", 21);
var employee = new Employee("David", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
var employeeOne = new EmployeeOne("DavidOne", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
var employeeTwo = new Employee("David", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
var employeeTwoPrototype = Employee.prototype;
var employeeThree = new Employee("David", 22, [
  "C",
  "C++",
  "Java",
  "Python",
  "PHP"
]);
console.log(employeeTwo.getSkills());