Javascript函数中的继承错误

Question

我以下列方式在JavaScript中应用继承:

var employee = function(name) {
  this.name = name;
}
employee.prototype.getName = function() {
  return this.name;
}
var pEmployee = function(salary) {
  this.salary = salary;
}
pEmployee.prototype.getSalary = function() {
  return this.salary;
}

var employee = new employee("mark");
pEmployee.prototype = employee;
var pe = new pEmployee(5000);
console.log(pe.getName());
console.log(pe.getSalary());

但它在控制台中显示以下错误:

未捕获的TypeError:pe.getSalary不是函数

谁能告诉我这个错误背后的原因是什么？

Answer 1

这是因为你已经添加getSalary到对象pEmployee.prototype引用,但随后完全被 pEmployee.prototype新对象替换.所以新对象自然没有getSalary.

您所展示的不是在ES5及更早版本中设置继承的正确方法.相反,请参阅内联注释:

var Employee = function(name) {
  this.name = name;
};
Employee.prototype.getName = function() {
  return this.name;
};

var PEmployee = function(name, salary) {
  // Note call to superclass
  Employee.call(this, name);
  // Now this level's initialization
  this.salary = salary;
};

// This sets up inheritance between PEmployee.prototype and
// Employee prototype (then fixes up the
// constructor property)
PEmployee.prototype = Object.create(Employee.prototype);
PEmployee.prototype.constructor = PEmployee;

// NOW you add the method
PEmployee.prototype.getSalary = function() {
  return this.salary;
};

// Usage
var employee = new Employee();
var pe = new PEmployee("Mark", 5000);
console.log(pe.getName());
console.log(pe.getSalary());

请参阅我的答案,以获得更全面的示例,以及使用ES2015 class语法时的样子.