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

有没有人能告诉我这个错误背后的原因是什么？

Answer 1

这是因为您已将getSalary添加到对象pEmployee.prototype所引用的内容，但随后完全替换了 pEmployee.prototype一个新对象。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my answer here以获取更全面的示例，以及使用ES2015的class语法时的情况。

Javascript函数中的继承错误

1 个答案: