重点：multipart/form-data 后端识别上传类型必填

1. form 表单上传

<!-- enctype="multipart/form-data" 这个必填 -->
<form action="http://127.0.0.1:8080/users/avatar" method="post" enctype="multipart/form-data"
><input name="name" type="text" /><input id="file" name="files" type="file" /><button>提交</button>
</form>
<script>const upload = document.getElementById("file");upload.onchange = function (value) {const fileList = value.target.files;console.log(fileList);};
</script>

2. js 上传

// 后端上传接口
function updateAvatar(data) {return api({url: "/users/avatar",method: "post",// 设置请求头(重点)headers: {"Content-Type": "multipart/form-data",},data,});
}let cutDown = (data) => {// 构建 form 表单;let formData = new FormData();let { file } = data;console.log(data);// file 参数命名和后端一致formData.append("file", file);updateAvatar(formData).then((res) => {console.log(res);});
};