js加载等待，js进度等待

//显示加载动画
function show_loading(){
var str='<div class="msg_bg" style="background:#000;opacity:0.5;filter:alpha(opacity=50);z-index:99998;width:100%;position:absolute;left:0;top:0"></div>';
str+='<div class="msg_bg" style="z-index:99999;width:100%;position:absolute;left:0;top:0;text-align:center;"><img src="img/loading.gif" alt="" class="loading"></div>'
$('body').append(str);
var scroll_height=$(document).scrollTop(); 
$('.msg_bg').height($(document).height());
$('.loading').css('margin-top',scroll_height+240);

}

点击按钮后执行上述方法；