var flag = false;
    var cur = {
        x:0,
        y:0
    }
    var nx,ny,dx,dy,x,y ;
    function down(){
        flag = true;
        var touch ;
        if(event.touches){
            touch = event.touches[0];
        }else {
            touch = event;
        }
        cur.x 
 
= touch.clientX;
        cur.y = touch.clientY;
        dx = div2.offsetLeft;
        dy = div2.offsetTop;
    }
    function move(){
        if(flag){
            var touch ;
            if(event.touches){
                touch = event.touches[0];
            }else {
                touch 
 
= event;
            }
            nx = touch.clientX - cur.x;
            ny = touch.clientY - cur.y;
            x = dx+nx;
            y = dy+ny;
            div2.style.left = x+"px";
            div2.style.top = y +"px";
            //阻止頁面的滑動默認事件
            document.addEventListener("touchmove
 
",function(){
                event.preventDefault();
            },false);
        }
    }
    var div2 = document.getElementById("div2");
    div2.addEventListener("mousedown",function(){
        down();
    },false);
    div2.addEventListener("touchstart",function(){
        down();
    },false)
    div2.addEventListener("mousemove",function(){
        move();
    },false);
    div2.addEventListener("touchmove",function(){
        move();
    },false)
    document.body.addEventListener("mouseup",function(){
        flag = false;
    },false);
    div2.addEventListener("touchend",function(){
        flag = false;
    },false)

適配 移動 pc 拖拽效果