http://www.cnblogs.com/lidabo/archive/2012/04/27/2473084.html
看评论大家都说老师的答案有问题，我查了查，发现只是我们too young too simple啊，原来是判断document.documentElement.clientHeight非零
function app2(x,y)
{ var sum,x,y;
sum = x * y;
return sum;
}
var req1=app2(5,6);
var req2=app2(2,3);
var sumq=req1+req2;
document.write("req1的值:"+req1+"<br/>");
document.write("req2的值:"+req2+"<br/>");
document.write(req1+"与"+req2+"和:"+sumq);
function checkone(){
var j=document.getElementById("wb").value;
// 任务3
var hobby = document.getElementsByName("hobby");
hobby[j-1].checked=true;
<script type="text/javascript">
var mystr="Hello World!";
var mynum=mystr.indexOf("o");
document.write(mystr.indexOf("o",mynum+1));
</script>
