js小问题 注释那三行 影响了return false的作用 请问是什么回事啊

<ul>
    <li>
        <a href="image/main1r1.png" onclick="showPic(this);return false;" title="main1r1" >main1r1</a>
    </li>
    <li>
        <a href="image/main2r2.png"  title="main2r2" onclick="showPic(this);return false;">main2r2</a>
    </li>
    <li>
        <a href="image/37.png" onclick="showPic(this);return false;" title="37">37</a>
    </li>
    <li>
        <a href="image/r3.png" title="r3" onclick="showPic(this);return false;">r3</a>
    </li>
</ul>
<img id="placeholder" src="image/logo2.gif" alt="my image gllay" />

function showPic( whichpic ){ var source = whichpic.getAttribute( 'href' ); var placeholder = document.getElementById( 'placeholder' ); placeholder.setAttribute( 'src',source ); //var text = whichpic.getAttribute( 'title' ); //var description = document.getElementById( 'description' ); //description.firstChild.nodeValue = text; }

你可以打断点看看是不是这三句有错误导致程序停止，或者添加alert测试，只有这三句有错才会导致后面的return false执行不到