面向对象的JavaScript-002

1.

 1 <script type="text/javascript">
 2
 3     // Define the Person constructor
 4     var Person = function(firstName) {
 5       this.firstName = firstName;
 6     };
 7
 8     // 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.
 9     var Person = function(firstName) {
10       if (this instanceof Person) {
11         this.firstName = firstName;
12       } else {
13         return new Person(firstName);
14       }
15     }
16
17     // Add a couple of methods to Person.prototype
18     Person.prototype.walk = function(){
19       console.log("I am walking!");
20     };
21
22     Person.prototype.sayHello = function(){
23       console.log("Hello, I‘m " + this.firstName);
24     };
25
26     // Define the Student constructor
27     function Student(firstName, subject) {
28       // Call the parent constructor, making sure (using Function#call)
29       // that "this" is set correctly during the call
30       Person.call(this, firstName);
31
32       // Initialize our Student-specific properties
33       this.subject = subject;
34     }
35
36     // Create a Student.prototype object that inherits from Person.prototype.
37     // Note: A common error here is to use "new Person()" to create the
38     // Student.prototype. That‘s incorrect for several reasons, not least
39     // that we don‘t have anything to give Person for the "firstName"
40     // argument. The correct place to call Person is above, where we call
41     // it from Student.
42     Student.prototype = Object.create(Person.prototype); // See note below
43
44     // Set the "constructor" property to refer to Student
45     Student.prototype.constructor = Student;
46
47     // Replace the "sayHello" method
48     Student.prototype.sayHello = function(){
49       console.log("Hello, I‘m " + this.firstName + ". I‘m studying "
50                   + this.subject + ".");
51     };
52
53     // Add a "sayGoodBye" method
54     Student.prototype.sayGoodBye = function(){
55       console.log("Goodbye!");
56     };
57
58     // Example usage:
59     var student1 = new Student("Janet", "Applied Physics");
60     student1.sayHello();   // "Hello, I‘m Janet. I‘m studying Applied Physics."
61     student1.walk();       // "I am walking!"
62     student1.sayGoodBye(); // "Goodbye!"
63
64     // Check that instanceof works correctly
65     console.log(student1 instanceof Person);  // true
66     console.log(student1 instanceof Student); // true
67
68     // 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:
69     function createObject(proto) {
70         function ctor() { }
71         ctor.prototype = proto;
72         return new ctor();
73     }
74
75     // Usage:
76     Student.prototype = createObject(Person.prototype);