点击加1代码
原理：
<input type="submit" value="点我增加数字" onclick="document.getElementById('count').innerHTML=parseInt(document.getElementById('count').innerHTML)+1"> <span id="count">1</span>
精简：
<input type="submit" value="点我增加数字" onclick="document.getElementById('count').innerHTML=parseInt(document.getElementById('count').innerHTML)+1"> <span id="count">1</span>
注：parseInt函数是指将字符转换成int型
if you don't try,you will never know!
