<form name="theform">
<input name="username" value="经典论坛">
</form>
<br><br>
<div id="a1"><a href="javascript:document.theform.username.value='大家好';void(0);">链接一</a></div>
<br>
<div id="a2"><a href="javascript:document.theform.username.value='你们好';void(0);">链接二</a></div>
<input name="username" value="经典论坛">
</form>
<br><br>
<div id="a1"><a href="javascript:document.theform.username.value='大家好';void(0);">链接一</a></div>
<br>
<div id="a2"><a href="javascript:document.theform.username.value='你们好';void(0);">链接二</a></div>
也可以用onclick事件
function but1(var a )
{
if ( a == "1")
document.theform.username.value='大家好';
else
document.theform.username.value='你们好';
}</script><input type=submit onclick=but1("1") value=submit name=submit>