JS——简单的登录框提示

<input type="text" id="uname" onfocus="showTip()" onblur="hideTip()">
	<span id="uname-show"></span>

	<script>
		function $(id){
			return document.getElementById(id);
		}

		function showTip(){
			$("uname-show").innerHTML = "用户名6-18位";
		}

		function hideTip(){
			if($("uname").value == ""){   //注意这里是value
				$("uname-show").innerHTML = "用户名不能为空";
			}else{
				$("uname-show").innerHTML = "通过";
			}
		}
	</script>