新人提出的简单问题!进来看看

Question

<SCRIPT LANGUAGE="JavaScript">
function aaa()
{
  var a=document.all.img1;  //img1为一IMG的ID
  if( a.src=="http://community.csdn.net/logo/images/prj.210.67.gif")
 {
    a.src="http://zi.csdn.net/bohan300-60.gif";

  }
else
  {
    a.src="http://community.csdn.net/logo/images/prj.210.67.gif";
  }
}
</SCRIPT>
<img id="img1"  name="Pre_Img"  border='0' src="http://community.csdn.net/logo/images/prj.210.67.gif" alt="请保护好自己的眼睛" width="210" height="67" />
<input type="button" value="change" onclick="aaa();">