Vue.js 在vue中使用axios上载图像，未找到文件

我试图用axios和express fileupload上传图像，但我不确定我在这里遗漏了什么，不起作用，控制台中“找不到文件”，有时出现错误500

这是我的密码：

<input type="file" name="file" class="hidden" ref="update_avatar_input" @change="update_avatar" accept="image/*">
<vs-button type="border" class="mr-4" @click="$refs.update_avatar_input.click()">Change Avatar</vs-button>


update_avatar (event) { 
      this.loading = true 
      const file = event.target.files || event.dataTransfer.files
      if (!file.length) return 
      const formData = new FormData()
      formData.set('file', event.target.files[0]) 
      formData.set('id', this.data_local.id)

      axios.post('http://localhost:8081/api/users/imgupload', formData, { 
        headers: {'Content-Type': 'multipart/form-data'} 
      }).then(response => { 
        if (response.data.error) {
          console.log('error', response.data.error)
        } else {
          console.log('success', response.data.message) 
          this.avatar = `/server/uploads/${event.target.files[0].name}`
        }
      }).catch(error => {
        console.log(error.response)
      })
      
    }

router.post('/imgupload', imgupload)

imgupload: (req, res) => {
     
    if (!req.files) {
      return res.status(500).send({ msg: 'file is not found' })
    }
    // accessing the file
    const myFile = req.files.file

    //  mv() method places the file inside public directory
    myFile.mv(`/server/uploads/${myFile.name}`, function (err) {
      if (err) {
        console.log(err)
        return res.status(500).send({ msg: 'Error occured' })
      }
      // returing the response with file path and name
      return res.send({name: myFile.name, path: `/${myFile.name}`})
    }) 
  }