<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<!--使用 prototype 属性可以向对象添加属性：-->
<script type="text/javascript">
function employee(name,job,born)
{
this.name=name;
this.job=job;
this.born=born;
}
var bill=new employee("Bill Gates","Engineer",1985);
employee.prototype.salary=null;
bill.salary=20000;
employee.prototype = {
testProperty:"zhangjie"
}/*这样做不会删除原来的属性，原因在于prototype只是用来添加属性的，并不会删除属性*/
var newOne = new employee();
document.write(bill.salary);/*正常显示2000*/
document.write(bill.testProperty); /*undefined*/ /*testProperty属性是在bill之后才设定的，*/
document.write(newOne.name);/*undefined未定义*/
document.write(newOne.testProperty);/*zhangjie*/ /*正常显示*/
</script>
</body>
</html>
