JavaScript如何获取鼠标移入div的方向

function getDirection(ev) {
            var mx = ev.clientX,
                    my = ev.clientY;
            var el = this.offsetLeft,
                    et = this.offsetTop,
                    ew = this.clientWidth,
                    eh = this.clientHeight;
            var left = mx - el,
                    right = el + ew - mx,
                    top = my - et,
                    bottom = et + eh - my;
            var min = Math.min.apply(Math, [left, right, top, bottom]);
            if (min === left) {
                    return "left";
            } else if (min === right) {
                    return "right";
            } else if (min === top) {
                    return "top"
            } else {
                    return "bottom";
            }
    }