Placeholder是HTML5新增的另一个属性，当input或者textarea设置了该属性后，该值的内容将作为灰字提示显示在文本框中，当文本框获得焦点时，提示文字消失。以前要实现这效果都是用JavaScript来控制才能实现：
<input id="t1" type="text" placeholder="请输入文字" />
让其他浏览器兼容这一效果方案：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB2312">
<title>验证Valid ----placeholder</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<style>
span.emptyhint {color:#999;position:absolute;padding:3px;}
</style>
</head>
<body>
<div id=doc3>
<div id="bd" >
<div class="section-ctn">
<ul>
<li>
<label class="k">订单主人：</label>
<input type="text" placeholder="请填写订单主人" value="JK">
</li>
<li>
<label class="k">订单号：</label>
<input type="text" placeholder="请填写订单号">
</li>
<li>
<label class="k">备注：</label>
<textarea type="text" placeholder="请填写备注"></textarea>
</li>
</ul>
</div>
</div>
</div>
</body>
<script>
function initPlaceHolders(){
if('placeholder' in document_createElement_x_x('input')){ //如果浏览器原生支持placeholder
return ;
}
function target (e){
var e=e||window.event;
return e.target||e.srcElement;
};
function _getEmptyHintEl(el){
var hintEl=el.hintEl;
return hintEl && g(hintEl);
};
function blurFn(e){
var el=target(e);
if(!el || el.tagName !='INPUT' && el.tagName !='TEXTAREA') return;//IE下，onfocusin会在div等元素触发
var emptyHintEl=el.__emptyHintEl;
if(emptyHintEl){
//clearTimeout(el.__placeholderTimer||0);
//el.__placeholderTimer=setTimeout(function(){//在360浏览器下，autocomplete会先blur再change
if(el.value) emptyHintEl.style.display='none';
else emptyHintEl.style.display='';
//},600);
}
};
function focusFn(e){
var el=target(e);
if(!el || el.tagName !='INPUT' && el.tagName !='TEXTAREA') return;//IE下，onfocusin会在div等元素触发
var emptyHintEl=el.__emptyHintEl;
if(emptyHintEl){
//clearTimeout(el.__placeholderTimer||0);
emptyHintEl.style.display='none';
}
};
if(document.addEventListener){//ie
document.addEventListener('focus',focusFn, true);
document.addEventListener('blur', blurFn, true);
}
else{
document.attachEvent('onfocusin',focusFn);
document.attachEvent('onfocusout',blurFn);
}
var elss=[document.getElementsByTagName_r('input'),document.getElementsByTagName_r('textarea')];
for(var n=0;n<2;n++){
var els=elss[n];
for(var i =0;i<els.length;i++){
var el=els[i];
var placeholder=el.getAttribute('placeholder'),
emptyHintEl=el.__emptyHintEl;
if(placeholder && !emptyHintEl){
emptyHintEl=document_createElement_x_x('span');
emptyHintEl.innerHTML=placeholder;
emptyHintEl.className='emptyhint';
emptyHintEl.onclick=function (el){return function(){try{el.focus();}catch(ex){}}}(el);
if(el.value) emptyHintEl.style.display='none';
el.parentNode.insertBefore(emptyHintEl,el);
el.__emptyHintEl=emptyHintEl;
}
}
}
}
initPlaceHolders();
</script>
</html>
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