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);