Скроллинг внутри div-а

x2 = 0;
y2 = 0;
x1 = 0;
y1 = 0;
prev_top = 0;
 
document.ontouchmove = tch_move;
document.ontouchstart = tch_start;
document.ontouchend = tch_end;
function tch_move(event){
    event.preventDefault();
    
    x1 = event.touches[0].clientX;
    y1 = event.touches[0].clientY;
}
 
 
scrolltch = 0;
function tch_start(){
    scrolltch = 1;
}
 
function tch_end(event){
    scrolltch = 0;
}
 
function main(){
 
    if (scrolltch == 1){
    
         elem = document.getElementById('center_scroll');
 
        if (y1 - y2 != 0){
            y3 = y1 - y2;
            prev_top += y3;
            elem.style.top = prev_top + "px";
            elem.innerHTML = prev_top;
        }
        x2 = x1;
        y2 = y1;
    }
}
setInterval('main()', 1);

див.onmousedown = function(down){
    var clickX = down.pageX,
    clickY = down.pageY,
    self = this,
    XLeft = window.getComputedStyle(this).top,YLeft,
    XTop = window.getComputedStyle(this).top,YTop;
    this.onmousemove = function(move){
         YLeft = move.pageX - clickX,
         YTop = move.pageY - clickY,
         self.style.Left = XLeft + YLeft + 'px',
         self.style.top = XTop + YTop + 'px';
    };
};