微信开发工具使用uploadFile上传文件的时候，formData里为什么没有东西？

upload() {
    wx.chooseImage({
      count: 1,
      success: chooseRes => {
        const tempFilePaths = chooseRes.tempFilePaths
        console.log(tempFilePaths);
        wx.uploadFile({
          url: 'https://example.com/upload_image?a=1',
          filePath: tempFilePaths[0],
          name: 'file',
          success: console.log,
          fail: console.log
        })
      }
    });
  }

只有query没有formData