h5微网页滑动

function da() {

        /*知道手指滑动*/
        var startx, starty;
        //获得角度
        function getAngle(angx, angy) {
            return Math.atan2(angy, angx) * 180 / Math.PI;
        };
        //根据起点终点返回方向 1向上 2向下 3向左 4向右 0未滑动
        function getDirection(startx, starty, endx, endy) {
            var angx = endx - startx;
            var angy = endy - starty;
            var result = 0;
//如果滑动距离太短
            if (Math.abs(angx) < 2 && Math.abs(angy) < 2) {
                return result;
            }
            var angle = getAngle(angx, angy);
            if (angle >= -135 && angle <= -45) {
                result = 1;
            } else if (angle > 45 && angle < 135) {
                result = 2;
            } else if ((angle >= 135 && angle <= 180) || (angle >= -180 && angle < -135)) {
                result = 3;
            } else if (angle >= -45 && angle <= 45) {
                result = 4;
            }
            return result;
        }
        //手指接触屏幕
        document.addEventListener("touchstart", function(e) {
            startx = e.touches[0].pageX;
            starty = e.touches[0].pageY;
        }, false);
        //手指离开屏幕
        document.addEventListener("touchend", function(e) {
            var endx, endy;
            endx = e.changedTouches[0].pageX;
            endy = e.changedTouches[0].pageY;
            var direction = getDirection(startx, starty, endx, endy);
            switch (direction) {
                case 0:
                    alert("未滑动！");
                    break;
                case 1:
                    alert("向上！");
                    break;
                case 2:
                    alert("向下！");
                    break;
                case 3:
                    alert("向左！");
                    break;
                case 4:
                    alert("向右！");
                    break;
                default:
            }
        }, false);

    }