置顶

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$(function(){

    $("body").append('<div class="r_ad" id="r_ad"><span id="r_ad1"></span></div>');

    $(window).scroll(function(){

        itemshow($(this));

    })

    function itemshow(el){

        var el=el||$(window)

        var item=$("#r_ad");

        if(el.scrollTop()>=200){

            item.show();

            return;

        }

            item.hide();

    }

    function roll(ele,itemnum,later){

        $(ele).animate({scrollTop: itemnum}, later);

    }  

    $("#r_ad1").click(function(){

        roll("html,body",0,700)

    });

});