Node.js写入现有地理位置JSON错误

我试图习惯于nodejs的基础，我试图将数据推送到现有的JSON文件，但是我得到了无法读取的属性'push'，未定义。

产品编号：

    var obj = {
       table: []
    };
        var app =  express();    
        app.get('/parseData', function (req, res) {
              var fs = require('fs');
              fs.readFile('./json/locationData.json', 'utf8', function readFileCallback(err, data){
                  if (err){
                      console.log(err);
                  } else {
                  obj = JSON.parse(data); //now it an object
                  obj.table.push({ "type": "Feature",
                    "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
                    "properties": {"prop0": "value0"}}
                  ); //add some data
                  json = JSON.stringify(obj); //convert it back to json
                  fs.writeFile('./json/locationData.json', json, 'utf8', callback); // write it back
res.header("Content-Type",'application/json');
      res.send(json);
              }});
            });
            app.listen(3000);

JSON文件：

 { "type": "FeatureCollection",
      "features": [
        { "type": "Feature",
          "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
          "properties": {"prop0": "value0"}
          },
         { "type": "Feature",
          "geometry": {"type": "Point", "coordinates": [103.0, 0.5]},
          "properties": {"prop0": "value0"}
          }
        ]
      }

[table从JSON文件中丢失

Node.js写入现有地理位置JSON错误

我试图习惯于nodejs的基础，我试图将数据推送到现有的JSON文件，但是我得到了无法读取的属性'push'，未定义。

产品编号：

    var obj = {
       table: []
    };
        var app =  express();    
        app.get('/parseData', function (req, res) {
              var fs = require('fs');
              fs.readFile('./json/locationData.json', 'utf8', function readFileCallback(err, data){
                  if (err){
                      console.log(err);
                  } else {
                  obj = JSON.parse(data); //now it an object
                  obj.table.push({ "type": "Feature",
                    "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
                    "properties": {"prop0": "value0"}}
                  ); //add some data
                  json = JSON.stringify(obj); //convert it back to json
                  fs.writeFile('./json/locationData.json', json, 'utf8', callback); // write it back
res.header("Content-Type",'application/json');
      res.send(json);
              }});
            });
            app.listen(3000);

JSON文件：

 { "type": "FeatureCollection",
      "features": [
        { "type": "Feature",
          "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
          "properties": {"prop0": "value0"}
          },
         { "type": "Feature",
          "geometry": {"type": "Point", "coordinates": [103.0, 0.5]},
          "properties": {"prop0": "value0"}
          }
        ]
      }

[table从JSON文件中丢失