老蔡写的代码，借鉴下！

var $info_b=$('div.info_b'),$xiaoxi = $info_b.find('div.xt-xiaoxi');

function DSQ(){
$('#'+footid).hide();

$xiaoxi.css({'position':'absolute','bottom':'0'})
.find('.xiaoxi').css({'width':'75%'});
$info_b.css({'position':'absolute','bottom':'0','borderTop':'1px solid #efefef'})
.find('.xiaoxi-btn').css({'display':'inline-block'});
$('.info_t_ul').css({'paddingBottom':'20'});
};

function UDSQ(){
$('#'+footid).show();

$xiaoxi.css({'bottom': '44','position':'fixed'})
.find('.xiaoxi').css({'width':'100%'});
$info_b.css({'bottom': '44','position':'fixed','left':0,'right':0})
.find('.xiaoxi-btn').css({'display':'none'});
$('.info_t_ul').css({'paddingBottom':'90'});
};

$xiaoxi.find('.xiaoxi').on('click',function(event){
event.stopPropagation();
event.preventDefault();
this.focus();
});

$xiaoxi.find('.xiaoxi').focus(
function(){
var scrollHeight=document.body.scrollHeight;
var speed=200;//滑动的速度
var OdocHeight=$(document).height()
$('body,html').animate({scrollTop:OdocHeight },speed);
setTimeout(DSQ,300);
});

$(document).on('click touchstart','.info_t',function(){
UDSQ();
$xiaoxi.find('.xiaoxi').blur();
});