//引入jQuery框架
$(function(){    if(!(‘placeholder‘ in document.createElement(‘input‘))){        jQuery(‘:input[placeholder]‘).each(function(index, element) {               var self = $(this), txt = self.attr(‘placeholder‘);               self.wrap($(‘<div></div>‘).css({position:‘relative‘,float:‘left‘, zoom:‘1‘, border:‘none‘, background:‘none‘, padding:‘none‘, margin:‘none‘}));               var pos = self.position(), h = self.outerHeight(true), paddingleft = self.css(‘padding-left‘);               var holder = $(‘<span></span>‘).text(txt).css({‘position‘:‘absolute‘,                                   ‘left‘:pos.left, ‘top‘:pos.top,                                   ‘height‘:h, ‘line-Height‘:h+‘px‘,                                   ‘paddingLeft‘:paddingleft, ‘color‘:‘#aaa‘}).appendTo(self.parent());               self.focusin(function(e) {                   holder.hide();               }).focusout(function(e) {                   if(!self.val()){                       holder.show();                   }else{                	   holder.hide();                   }               });               holder.click(function(e) {                   holder.hide();                   self.focus();               });           });   }});