如何用javascript判断用户填写注册信息是否完整?

[huguang]

我是菜鸟！
最好能给个简单的实例！
谢谢各位！！！

[vvfish119]

<script language="javascript">
function change() {
if (form1.text1.value=="")
{alert("用户名不能为空！");}
else{form1.sumbit;}
}
</script>
<form action="#" name="form1" method="post">
<input type=text name="text1">
<input type="button" onClick="change();" value="提交">
</form>

[lxyy_1118]

<script language="javascript">
function change() {
function check()
{
if (form1.text1.value=="")
{alert("用户名不能为空！");
return true;
}
else return false;
}
</script>
<form action="xxx.asp" name="form1" method="post" onsubmit="return check();">
<input type=text name="text1">
<input type="submit" name="button1" value="提交">
</form>

[alphaltx]

<script language="javascript">
function change() {
if (form1.text1.value==""){
alert("用户名不能为空！");
form1.text1.focus();
}else{
form1.sumbit;
}
}
</script>

<form action="xxxx" name="form1" method="post">
<input type=text name="text1" id="text1">
<input type="button" onClick="change();" value="提交">
</form>