prototype
prototype属性允许您向任何对象添加属性和方法（Number，Boolean，String和Date等）。
Note - Prototype是一个全局属性，几乎可用于所有对象。
使用以下语法创建布尔原型。
object.prototype.name = value
例子 (Example)
以下示例显示如何使用prototype属性向对象添加属性。
<html>
<head>
<title>User-defined objects</title>
<script type = "text/javascript">
function book(title, author){
this.title = title;
this.author = author;
}
</script>
</head>
<body>
<script type = "text/javascript">
var myBook = new book("Perl", "Tom");
book.prototype.price = null;
myBook.price = 100;
document.write("Book title is : " + myBook.title + "<br>");
document.write("Book author is : " + myBook.author + "<br>");
document.write("Book price is : " + myBook.price + "<br>");
</script>
</body>
</html>
成功执行上述代码后，将显示以下输出。
Book title is : Perl
Book author is : Tom
Book price is : 100
