jquery兑现验证表单非空 _Web前端

jquery实现验证表单非空
表单验证非空，包括空格验证，贴代码：

<html>
<head>
	<title>input</title>
	<script type="text/javascript" src="jquery.min.js"></script>
	<script type="text/javascript">
		$(document).ready(function(){
			$('#error').hide();
			$('#submit').click(function(event){
				var data = $('#userId').val();
				data = $.trim(data);
				if(data.length < 1) {
					$('#error').show();
					event.preventDefault();
				} else {
					$('#error').hide();
				}
			});
		});
	</script>
</head>
<body>
	<form id="signup" method="post" action="">
		user id:<input type="text" id="userId" name="userId" /><span id="error">this field can't be blank</span><br/>
		<input type="submit" id="submit" value="Submit">
	</form>
</body>
</htmL>