js判断元素滑动方向（上下左右）移动端

每天学习一点点。

 1 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);

原文地址：http://www.cnblogs.com/beiz/p/5817192.html