<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script type="text/javascript" src="js/jquery-1.4.2.min.js"></script>
<script type="text/javascript">
//第一种方法
$(document).ready(function(){
var doc=document,inputs=doc.getElementsByTagName('input'),supportPlaceholder='placeholder'in doc.createElement('input'),placeholder=function(input){var text=input.getAttribute('placeholder'),defaultValue=input.defaultValue;
if(defaultValue==''){
input.value=text}
input.onfocus=function(){
if(input.value===text){this.value=''}};
input.onblur=function(){if(input.value===''){this.value=text}}};
if(!supportPlaceholder){
for(var i=0,len=inputs.length;i<len;i++){var input=inputs[i],text=input.getAttribute('placeholder');
if(input.type==='text'&&text){placeholder(input)}}}});
//第二种方法
$(function(){
if(!placeholderSupport()){ // 判断浏览器是否支持 placeholder
$('[placeholder]').focus(function() {
var input = $(this);
if (input.val() == input.attr('placeholder')) {
input.val('');
input.removeClass('placeholder');
}
}).blur(function() {
var input = $(this);
if (input.val() == '' || input.val() == input.attr('placeholder')) {
input.addClass('placeholder');
input.val(input.attr('placeholder'));
}
}).blur();
};
})
function placeholderSupport() {
return 'placeholder' in document.createElement('input');
}
</script>
</head>
<body>
<form>
<label for="name">用户名：</label>
<input type="text" placeholder="请输入用户名"/>
</form>
</body>
</html>