<form action="#" method="post" name="form01">
<p>用户：<input type="text" name="username"></p>
</form>
<script>
form01.elements[0].style.background='red'
</script>

<form action="#" method="post" name="form02">
<p>用户：<input type="text" name="username"></p>
<p>密码：<input type="password" name="password"></p>
<p><input type="submit" value="提交"></p>
</form>
<script>
var fele=form02.elements
for(var i=0;i<fele.length;i++){
var e=fele[i]
if(e.type=='submit'){
e.style.background='red'
}else{
e.style.background='orange'
}
}
</script>