js实现返回页面顶部

window.scrollTo(0,0);

$(window).scrollTop(0);

function smoothscroll(){   
         window.requestAnimationFrame(smoothscroll);  
         window.scrollTo (0,currentScroll - (currentScroll/5));  
}

$('html,body').animate({scrollTop:0},200);

if($('html').scrollTop()){
    $('html').animate({scrollTop:0},200);
    return false;
}
$('body').animate({scrollTop:0},200);
return false;