移动端拖动元素（盒子初始距离，加上移动距离（move的e.pagexy-start的e.pagexy）.)

   <script>
        window.addEventListener('load', function () {
            var div = document.querySelector('div');


            var startx = 0;
            var starty = 0;
            var x = 0;
            var y = 0;

            div.addEventListener('touchstart', function (e) {
                startx = e.targetTouches[0].pageX;
                starty = e.targetTouches[0].pageY;
                x = this.offsetLeft;
                y = this.offsetTop;
                // console.log(startx, starty);
            })


            div.addEventListener('touchmove', function (e) {

                movex = e.targetTouches[0].pageX;
                movey = e.targetTouches[0].pageY;
                // movex减startx为盒子移动距离，还得再加上初始距离
                this.style.left = x + movex - startx + 'px';
                this.style.top = y + movey - starty + 'px';
    e.preventDefault(); // 阻止因为touchmove屏幕滚动的默认行为

            })


        })

    </script>