js判断提交的表单是否为空

<script>
function check()
{
if(document.form.name.value=="")
{
alert("请输入用户名");
document.form.name.focus();
return false;
}

var form=document.getElementById("form");
form.submit();
return true;
}
</script>

<form name="form" id="form" action="../addUserOneServlet" method="post">

<input type="text" name="name"  value="">

<input type="button"  onclick="check()" value="保存" ><input type="reset"  value="重置"><input type="button"  value="返回" onclick="javascript:history.go(-1);">

</form>