gistfile1.txt

//CS Blazor WebAssembly Part:
public static class FileUtil
	{
		public static IEnumerable<List<T>> Partition<T>(this IList<T> source, Int32 size)
		{
			for (int i = 0; i < Math.Ceiling(source.Count / (Double) size); i++)
			{
				yield return new List<T>(source.Skip(size * i).Take(size));
			}
		}

		public static async ValueTask SaveAs(this IJSRuntime js, string filename, byte[] data)
		{
			var key = Guid.NewGuid().ToString();
			foreach (var partFile in Partition(data, 3125000))
			{
				await js.InvokeVoidAsync(
					"saveAsFileAddBuffer",
					key,
					partFile);
			}
			await js.InvokeVoidAsync(
				"saveBuffer",
				filename,
				key);
		}
}

//js Part:
_buffer = new Array();

function saveAsFileAddBuffer(key, bytesBase64) {
    var filter = _buffer.filter(e => e.Key == key);

    if (filter.length === 0) {
        filter = {
            Key: key,
            Buffer: new Array()
        };
        _buffer.push(filter);
    } else {
        filter = filter[0];
    }
    filter.Buffer.push(bytesBase64);
}


function saveBuffer(filename, key) {
    console.log("Save " + key);
    
    var filter = _buffer.filter(e => e.Key == key)[0];
    var parts = new Array();

    for (var base64Part in filter.Buffer) {
        var bytes = new Uint8Array(base64Part.length);
        for (var i = 0; i < base64Part.length; i++) {
            bytes[i] = base64Part.charCodeAt(i);
        }
        parts.push(bytes);
    }
    _buffer.splice(_buffer.indexOf(filter), 1);

    var blob = new Blob(parts, { type: "application/octet-stream" });
    if (navigator.msSaveBlob) {
        //Download document in Edge browser
        navigator.msSaveBlob(blob, filename);
    }
    else {
        var link = document.createElement('a');
        link.download = filename;
        link.href = URL.createObjectURL(blob);
        document.body.appendChild(link); // Needed for Firefox
        link.click();
        document.body.removeChild(link);
    }
}