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;
 2     //获得角度
 3     function getAngle(angx, angy) {
 4         return Math.atan2(angy, angx) * 180 / Math.PI;
 5     };
 6  
 7     //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
 8     function getDirection(startx, starty, endx, endy) {
 9         var angx = endx - startx;
10         var angy = endy - starty;
11         var result = 0;
12  
13         //如果滑动距离太短
14         if (Math.abs(angx) < 2 && Math.abs(angy) < 2) {
15             return result;
16         }
17  
18         var angle = getAngle(angx, angy);
19         if (angle >= -135 && angle <= -45) {
20             result = 1;
21         } else if (angle > 45 && angle < 135) {
22             result = 2;
23         } else if ((angle >= 135 && angle <= 180) || (angle >= -180 && angle < -135)) {
24             result = 3;
25         } else if (angle >= -45 && angle <= 45) {
26             result = 4;
27         }
28  
29         return result;
30     }
31     //手指接触屏幕
32     document.addEventListener("touchstart", function(e) {
33         startx = e.touches[0].pageX;
34         starty = e.touches[0].pageY;
35     }, false);
36     //手指离开屏幕
37     document.addEventListener("touchend", function(e) {
38         var endx, endy;
39         endx = e.changedTouches[0].pageX;
40         endy = e.changedTouches[0].pageY;
41         var direction = getDirection(startx, starty, endx, endy);
42         switch (direction) {
43             case 0:
44                 alert("未滑动！");
45                 break;
46             case 1:
47                 alert("向上！")
48                 break;
49             case 2:
50                 alert("向下！")
51                 break;
52             case 3:
53                 alert("向左！")
54                 break;
55             case 4:
56                 alert("向右！")
57                 break;
58             default:
59         }
60     }, false);