Multifile upload as chunks

问题:

I'm setting up multi file upload in client-side.Below are the steps, I need to done:

1. User will upload multiple files at once. Ex: 5 files at a time.
2. Each file size is vary and large files. Ex: File1.size = 800mb
3. Slice that large files into chunks. Ex: chunk_size = 50mb
4. Each chunk will be send to backend and will get response from it.

I'm able to do it for single file upload, like splicing large file chunks.But I'm unable to do it for multiple files uploaded at a time.

Below is the code I tried:

var that = this;
var files = that.files || [];
var url = that.config.url;
var fileKeyUpload = that.config.fileKeyUpload;
for(var i=0; i < files.length; i++) {  //multiple files loop
    var start = 0;    //chunk start as 0
    var bytes_per_chunk = 52428800; // 50 MB  per chunk
    var blob = files[i];
    var size = blob.size;
    var end = bytes_per_chunk;
    var getStatus = function() {
        var nextChunk = start + bytes_per_chunk;
        var percentage = nextChunk > size ? 100 : Math.round((start / size) * 100); // calculating percentage
        uploadFile(blob.slice(start, end), files[key], start, percentage).then(function() {
            if(start < size && bytes_per_chunk < size){
                start = end;
                end = start + bytes_per_chunk;
                start < size ? getStatus() : null;
            }
        });
    }
    return getStatus();
}

function uploadFile(blob, file, offset, completedPrecentile) {
    return new Promise(function(resolve) {
        var xhr = new XMLHttpRequest();
        xhr.open("POST", url);
        xhr.setRequestHeader("Accept", "*/*");
        xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
        xhr.onreadystatechange = function() {
            if (xhr.readyState === 4 && xhr.status === 200) {
                if(that.config.hasOwnProperty("onFileUploadComplete")){
                    that.config.onFileUploadComplete(xhr, true, completedPrecentile, file);
                    resolve();
                }
            }
        };
        xhr.send(blob);
    });
};

This is what I tried, it works for single file, Any help on how to achieve multiple file upload with slicing large files into chunks.

Unable to post working demo since local api is used.