比如，我们定义了一个Classroom对象，这里我们定一个事件，当教室里的人增加超60人时就触发一个事件onFull;具体定义如下：
var Classroom=function()
{
this.numberOfPeople=0;
this.onFull=null;
this.peopleEnter=function(number)
{
this.numberOfPeople+=number;
if(this.numberOfPeople>60&&this.onFull!=null)
{
this.onFull(this.numberOfPeople);
}
}
}
function show1(number)
{
alert("教室里有"+number+"人");
}
function show2(number)
{
alert("教室里超出了"+(number-60)+"人");
}
var classroom1=new Classroom();
classroom1.onFull=show1;
classroom1.peopleEnter(30);
classroom1.peopleEnter(32);
classroom1.onFull=show2;
classroom1.peopleEnter(34);