<script type="text/javascript" src="jquery-1.7.2.min.js">script> 
<script type="text/javascript" src="jquery.enplaceholder.js">script> 

//通過value模擬placeholder 
$('input').placeholder(); 
//通過插入元素模擬placeholder 
$('input').placeholder({isUseSpan:true}); 

 <script type="text/javascript" src="/demo/js/jquery.min.js"></script><script type="text/javascript" src="/demo/js/38/jquery.enplaceholder.js"></script>
<style type="text/css">
body { font: 12px/1.5 'simsun'; }
form { width: 420px; height: 260px; margin: 20px auto 0; }
h3 { font-weight: bold; margin: 10px 0; }
p { margin-bottom: 10px; }
input { vertical-align: middle; margin-left: 10px; height: 24px; line-height: 24px; width: 200px; padding-left: 2px; }
textarea { vertical-align: middle; margin-left: 10px; width: 200px; height: 50px; font: inherit; padding-left: 2px; }
.wrap-statistics { visibility: hidden; }
html{color:#000;background:#fff;}
body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,form,input,textarea,p,th,td,hr,button{margin:0;padding:0;}
body,button,input,select,textarea{font:12px/1.5 tahoma,arial;}
input,select,textarea{font-size:100%;}
table{border-collapse:collapse;border-spacing:0;}
th{text-align:inherit;}
img{border:0;}
iframe{display:block;}
em,th{font-style:normal;font-weight:500;}
ol,ul {list-style:none;}
h1,h2,h3,h4,h5,h6{font-size:100%;font-weight:500;}
a{text-decoration:none;}
a:hover{text-decoration:underline;}

.fn-clear{zoom:1;}
.fn-clear:after{visibility:hidden;display:block;font-size:0;content:".";clear:both;height:0;}
.fn-hide{display:none;}
.fn-left,.fn-right{display:inline;}
.fn-left{float:left;}
.fn-right{float:right;}
.fn-hide-text{font-size:0;line-height:0;color:rgba(0,0,0,0);}
.sl-wrap,.sl-wrap td,.sl-wrap th{word-wrap:break-word;word-break:break-all;} 
.sl-wrap-table{ table-layout:fixed; }</style>
<form id="form1">
 <h3>通過value方式模擬placeholder</h3>
 <p>$('#form1 input,#form1 textarea').placeholder();</p>
 <p><label for="username1">用戶名:</label> <input id="username1" name="username1" placeholder="請輸入用戶名" required="" type="text" value="" /></p>
 <p><label for="address1">地　址:</label> <input id="address1" name="address1" placeholder="請輸入地址" required="" type="text" value="" /></p>
 <p><label for="remarks1">備　注:</label></p>
</form>
<form id="form2">
 <h3>在不支持placeholder的瀏覽器下，通過插入懸浮的span元素方式模擬</h3>
 <h4>文本框內(nèi)容改變時placeholder消失:</h4>
 <p>$('#username2,#password').placeholder({isUseSpan:true});</p>
 <p><label for="username2">用戶名:</label> <input id="username2" name="username1" placeholder="請輸入用戶名" required="" type="text" value="" /></p>
 <p><label for="password">密　碼:</label> <input id="password" name="password" placeholder="請輸入密碼" required="" type="password" value="" /></p>
 <p><label for="remarks2">備　注:</label></p>
 <h4>獲得焦點時placeholder消失:</h4>
 <p>$('#address2').placeholder({isUseSpan:true,onInput:false});</p>
 <p><label for="address2">地　址:</label> <input id="address2" name="address1" placeholder="請輸入地址" required="" type="text" value="" /></p>
</form>
<script>
 $('#form1 input,#form1 textarea').placeholder();
 $('#username2,#password').placeholder({isUseSpan:true});
 $('#address2').placeholder({isUseSpan:true,onInput:false});
 $('#remarks2').placeholder({isUseSpan:true});
</script>