在Json中計數數組insinde數組

Question

我收到了這個JSON文件。路徑數組可以是從1到100，

{ 
"waypoints": [ 
    { 
     "path0": [ 
      { 
       "color": "#0000FF" 
      }, 
      { 
       "lat": "37.9875000", 
       "lon": "23.7609260" 
      }, 
      { 
       "lat": "37.9873130", 
       "lon": "23.7607460" 
      }, 
      { 
       "lat": "37.9873840", 
       "lon": "23.7604100" 
      } 
     ], 
     "path1": [ 
      { 
       "color": "#00FF00" 
      }, 
      { 
       "lat": "37.9873840", 
       "lon": "23.7604100" 
      }, 
      { 
       "lat": "37.9878040", 
       "lon": "23.7605670" 
      }, 
      { 
       "lat": "37.9882590", 
       "lon": "23.7607340" 
      } 
     ], 
     "path2": [ 
      { 
       "color": "#FF0000" 
      }, 
      { 
       "lat": "37.9882590", 
       "lon": "23.7607340" 
      }, 
      { 
       "lat": "37.9884690", 
       "lon": "23.7598760" 
      } 
     ] 
    } 
] 
} 

我怎麼能看到多少路（PATH0，PATH1，..）陣列我一定在裏面的Javascript waypoints？ 使用obj.waypoints.length將返回0.

謝謝。

Answer 1

在一個現代的瀏覽器，您可以用Object.keys：

var nbpaths = Object.keys(obj.waypoints[0]).length; 

對於IE8的兼容性，可以算這樣的：

var nbpaths = 0; 
for (var key in obj.waypoints[0]) nbpaths++;