判断手指滑动方向

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);