<html><head><script>
function Pet(){ // Base Class
var owner = "Mrs. Jones";
var gender = undefined;
this.setOwner = function(who) { owner=who; }; //1
this.getOwner = function(){ return owner; }
this.setGender = function(sex) { gender=sex; }
this.getGender = function(){ return gender; }
}
function Cat(){} //subclass constructor
Cat.prototype = new Pet();
Cat.prototype.constructor=Cat;
Cat.prototype.speak=function speak(){
return("Meow"); //2
}; //3
function Dog(){}; //4
Dog.prototype= new Pet();
Dog.prototype.constructor=Dog;
Dog.prototype.speak = function speak(){
return("Woof");
}; //5
</script></head>
<body><script>
var cat = new Cat;
var dog = new Dog;
cat.setOwner("John Doe");
cat.setGender("Female");
dog.setGender("Male");
document.write(
"<br>The cat is a "+ cat.getGender()+ " owned by "
+ cat.getOwner() +" and it says " + cat.speak());
document.write(
"<br>The dog is a "+ dog.getGender() + " "
+ " owned by " + dog.getOwner() + " and it says " + dog.speak());
</script></body>
//1
和//2
的行中,在结束花括号后,为什么会出现分号?//3
和//4
将被执行。嗯...... JavaScript不会在你的代码中将分号放在任何地方,编写脚本的人就是这样,对吧?然而,JavaScript做的是在你错过的空格中自动插入分号(不是在你的代码中,至少不是明显的。它会读取你的代码,然后它的行为就好像你在编写它时那些自动插入的分号一样)。这有时会产生意想不到的结果。
我建议在每个声明后使用分号,如这个伟大的//5
所述。
如果我正确理解你的第二个问题,那就是这样的: Javascript基于对象Pet的原型实例化新的Object。然后将Cat.prototype指向这个新创建的对象。在Dog的情况下也会发生同样的事情。