var alto, ancho, destination;


window.onload = function(){
    var divFlecha = document.getElementById('scrolltotop_parent');
    divFlecha.style.visibility = 'hidden';
    divFlecha.onclick = irArriba;
    alto = screen.height;
    ancho = screen.width;
    if(ancho <= 768){
        destination = alto - 100;
    }
    divFlecha.style.top ="destination"+"px;";

};


window.addEventListener('scroll',function(){

     if(ancho <= 768){
        if(window.pageYOffset >= alto){
                document.getElementById('scrolltotop_parent').style.visibility = 'visible';
        }
        else {
                document.getElementById('scrolltotop_parent').style.visibility = 'hidden';
        }
    }
 });


const obtener_pixeles_inicio = () => document.documentElement.scrollTop || document.body.scrollTop;

const irArriba = () => {

        if(obtener_pixeles_inicio() > 0){
                requestAnimationFrame(irArriba);
                scrollTo(0, obtener_pixeles_inicio() - (obtener_pixeles_inicio() / 20));
        }
}