面向对象的JavaScript-002

1.

 <script type="text/javascript">

     // Define the Person constructor
     var Person = function(firstName) {
       this.firstName = firstName;
     };

     // Making sure that this points to the right thing regardless of how the object is instantiated can be difficult. However, there is a simple idiom to make this easier.
     var Person = function(firstName) {
       if (this instanceof Person) {
         this.firstName = firstName;
       } else {
         return new Person(firstName);
       }
     }

     // Add a couple of methods to Person.prototype
     Person.prototype.walk = function(){
       console.log("I am walking!");
     };

     Person.prototype.sayHello = function(){
       console.log("Hello, I'm " + this.firstName);
     };

     // Define the Student constructor
     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;

     // Replace the "sayHello" method
     Student.prototype.sayHello = function(){
       console.log("Hello, I'm " + this.firstName + ". I'm studying "
                   + this.subject + ".");
     };

     // Add a "sayGoodBye" method
     Student.prototype.sayGoodBye = function(){
       console.log("Goodbye!");
     };

     // Example usage:
     var student1 = new Student("Janet", "Applied Physics");
     student1.sayHello();   // "Hello, I'm Janet. I'm studying Applied Physics."
     student1.walk();       // "I am walking!"
     student1.sayGoodBye(); // "Goodbye!"

     // Check that instanceof works correctly
     console.log(student1 instanceof Person);  // true
     console.log(student1 instanceof Student); // true

     // 如果 On older JavaScript engines without Object.create, one can either use a "polyfill" (aka "shim", see the linked article), or one can use a function that achieves the same result, such as:
     function createObject(proto) {
         function ctor() { }
         ctor.prototype = proto;
         return new ctor();
     }

     // Usage:
     Student.prototype = createObject(Person.prototype);