var id = 0
function sc(time){

    if(document.body.scrollTop > $(‘#xx‘).offsetTop) 
    {
        requestAnimationFrame(sc)
        document.body.scrollTop -= 8
    }    
    else 
        cancelAnimationFrame(id)
}


var $ = function(selecor){
    return document.querySelector(selecor)
}

function start(){
    id = requestAnimationFrame(sc)
}

start()