XMLHttpRequest提交form表单数据，包括上传文件

<input id="uploadFile" name="file" type="file">
<script>
 const file = document.getElementById('uploadFile')
        let formData = new FormData()
        formData.append('file', file.files[0])
        const req = new XMLHttpRequest()
        req.onreadystatechange = function(){
          if (req.readyState === 4) {
            const response  = JSON.parse(req.responseText)
            if (response.code === '200') {
              console.log('success')
            } else {
              console.log('fail')
            }
          }
        }
        req.open('post', 'https://sxxx.com/uploadfile', true)
        req.send(formData)
</script>