js的用setAttribute图片切换

<ul>
   <li>
      <a href="images/1.jpg" title="asd1" onclick="showPic(this);return false;">Firrworks</a>
   </li>
   <li>
      <a href="images/2.jpg" title="asd2" onclick="showPic(this);return false;">Firrworks1</a>
   </li>
   <li>
      <a href="images/3.jpg" title="asd3" onclick="showPic(this);return false;">Firrworks2</a>
   </li>
   <li>
      <a href="images/4.jpg" title="asd4" onclick="showPic(this);return false;">Firrworks3</a>
   </li>
</ul>

<img id="placeholder" src="images/5.jpg" alt="our  hello" >

function  showPic(Whichpic){


  var source=Whichpic.getAttribute("href");


  var placeholder=document.getElementById('placeholder');


  placeholder.setAttribute("src",source);
 
 }