Wechat applet server to obtain image and text information

(PHP+CI framework) Below, the information of the file can be easily obtained, but the information in the formData cannot be obtained.
For example, in the following sample program, there is formData:{'user': 'test'}. On the server side, you can use $_FILES[file] to get the data of the uploaded file itself. So how to get the data transmitted in formData?
wx.chooseImage({
  success: function(res) { var tempFilePaths = res.tempFilePaths
    wx.uploadFile({
      url: 'http://example.weixin.qq.com/upload', //just an example, not real Interface address
      filePath: tempFilePaths[0],
      name: 'file',

      formData:{ 

       'user': 'test'

      },

      success: function(res){        

var data = res.data        //do something

      }
    })
  }
})

Checked, formdata is stored in $_POST, such as the above case, on the server side:

_POST['user'];

You can get the value of $string to be 'test'.