<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>鼠标点击input框后里面的内容就消失</title>
</head>
<body>
<input type="text" size="18" value="这是默认的内容" onfocus="if (value =='这是默认的内容'){value =''}" onblur="if (value ==''){value='这是默认的内容'}" />
</body>
</html>