如何使用参数调用继承的JavaScript构造函数？

Question

问候,

阅读以下文章后,我有一个问题:https: //developer.mozilla.org/en/Introduction_to_Object-Oriented_JavaScript

在继承示例中,Person构造函数不接受任何参数.如果我要添加一个并从Student构造函数中调用它,那么同样的例子怎么样？

谢谢!

Answer 1

好吧,一种可以重用Person构造函数逻辑的方法是使用call或调用它apply,例如:

function Person(gender) {
  this.gender = gender;
}

function Student(gender) {
  Person.apply(this, arguments);
}
Student.prototype = new Person(); // make Student inherit from a Person object
Student.prototype.constructor = Student; // fix constructor property

var foo = new Student('male');
foo.gender;             // "male"
foo instanceof Student; // true
foo instanceof Person;  // true

如果你想在Person没有参数的情况下调用构造函数的执行(比如在行:) Student.prototype = new Person();,你可以检测到它,例如:

function Person(gender) {
  if (arguments.length == 0) return; // don't do anything
  this.gender = gender;
}

Answer 2

接受的答案似乎是不正确的.根据Mozilla关于OO JavaScript的说法,正确的方法是:

var Person = function(firstName) {
    this.firstName = firstName;
};

function Student(firstName, subject) {
  // Call the parent constructor, making sure (using Function#call)
  // that "this" is set correctly during the call
  Person.call(this, firstName);

  // Initialize our Student-specific properties
  this.subject = subject;
};

// Create a Student.prototype object that inherits from Person.prototype.
// Note: A common error here is to use "new Person()" to create the
// Student.prototype. That's incorrect for several reasons, not least 
// that we don't have anything to give Person for the "firstName" 
// argument. The correct place to call Person is above, where we call 
// it from Student.
Student.prototype = Object.create(Person.prototype); // See note below

// Set the "constructor" property to refer to Student
Student.prototype.constructor = Student;

// Example usage:
var student1 = new Student("Janet", "Applied Physics");

您可以清楚地看到,Mozilla指定使用"new Person()"创建Student.prototype是一个常见错误.因此,接受的答案具有误导性.

我实际上已经在我正在进行的项目中对此进行了测试,并且Mozilla的方式是正确的,而上述答案不起作用.