JQuery keyup

<li><label for="ZC_company">公司名称：</label><input type="text" id="com_name" name="com_name" value="" />
			<span class="correct" id="correct_company" style="display:none"></span>
		</li>

<script type="text/javascript">
$("#com_name").keyup(function(){
		var com_name = "";
		password = $("#com_name").val();
		if(password.length>0)
			$("#correct_company").show();
		else
			$("#correct_company").hide();
	});
</script>