html部分
<body>
<div class="search">
<input type="text" id="txt"/>
<label for="txt" id="message">必败的国际大牌</label>
</div>
</body>
css部分
<style> .search { width:300px; height: 30px; margin: 100px auto; position: relative; } .search input { width:200px; height:25px; } .search label { font-size: 12px; color:#ccc; position: absolute; top:8px; left:20px; cursor: text; } </style>
js部分
<script> window.onload = function(){ function $(id){return document.getElementById(id);} //oninput 大部分浏览器支持 检测用户表单输入内容 //onpropertychange ie678 检测用户表单输入内容 $("txt").oninput = $("txt").onpropertychange = function(){ if(this.value == " ") { $("message").style.display = "block"; } else { $("message").style.display = "none"; } } } </script>