vue大文件分片上传后 后端接收到了一个blob怎么回事，有没有大佬解释下？

Question

import axios from "axios";
const upload = (url, data, headers = {}) => {
return new Promise((resolve, reject) => {
    axios({
        url,
        method: "post",
        data,
        headers: {
            ...headers,
            'Content-Type': 'multipart/form-data'
        }
    }).then(res => {
        return resolve(res.data)
    }).catch(err => {
        return reject(err)
    })
})

}
//分片上传
const uploadByPieces = async (url,{ fileName, file }) => {

// 上传过程中用到的变量
const chunkSize = 5 * 1024 * 1024; // 5MB一片
const chunkCount = Math.ceil(file.size / chunkSize); // 总片数
// 获取当前chunk数据
const getChunkInfo = (file, index) => {
    let start = index * chunkSize;
    let end = Math.min(file.size, start + chunkSize);
    let chunk = file.slice(start, end);
    return { start, end, chunk };
};
// 分片上传接口
const uploadChunk = (data) => {
    return new Promise((resolve, reject) => {
        axios({
            url,
            method: "post",
            data,
            headers: {
                'Content-Type': 'multipart/form-data'
            }
        }).then(res => {
            return resolve(res.data)
        }).catch(err => {
            return reject(err)
        })
    })
}
// 针对单个文件进行chunk上传
const readChunk = (index) => {
    const { chunk } = getChunkInfo(file, index);
    let fetchForm = new FormData();
    fetchForm.append("chunk", chunk);
    fetchForm.append("index", index);
    fetchForm.append("chunkCount", chunkCount);
    return uploadChunk(fetchForm)
};
// 针对每个文件进行chunk处理
const promiseList = []
try {
    for (let index = 0; index < chunkCount; ++index) {
            promiseList.push(readChunk(index))
    }
    const res = await Promise.all(promiseList)
    return res
}catch (e) {
    return e
}
}

export { upload, uploadByPieces }