FileSize em C# e JavaScript

FileSize.cs

public static class LongExtensions
{
    private static readonly string[] Sizes = { "bytes", "KB", "MB", "GB", "TB" };
    public static string ToFileSize(this long? bytesSize) => bytesSize.HasValue ? ToFileSize(bytesSize.Value) : "0 bytes";

    public static string ToFileSize(this long bytesSize) => SizeWithMaxSize.TakeWhile(e => bytesSize >= e.Item2).Select(size=> $"{bytesSize / size.Item2:0.#} {size.Item1}").Last();

    private static IEnumerable<Tuple<string, double>> SizeWithMaxSize => Sizes.Select((s, i) => new Tuple<string, double>(s, Pow(1024, i)));
}

FileSize.js

function toFileSize(bytesSize) {
    bytesSize = isNaN(bytesSize) ? 0 : bytesSize;
    var oneByte = 1;
    var kiloByte = oneByte * 1024;
    var megaByte = kiloByte * 1024;
    var gigaByte = megaByte * 1024;
    var teraByte = gigaByte * 1024;

    var size, unit;

    if (bytesSize >= teraByte) {
        size = Math.round(bytesSize / teraByte, 1);
        unit = 'TB';
    } else if (bytesSize >= gigaByte) {
        size = bytesSize / gigaByte;
        unit = 'GB';
    } else if (bytesSize >= megaByte) {
        size = bytesSize / megaByte;
        unit = 'MB';
    } else if (bytesSize >= kiloByte) {
        size = bytesSize / kiloByte;
        unit = 'KB';
    } else {
        size = bytesSize / oneByte;
        unit = 'bytes';
    }
    size = Math.round(size * 100) / 100;
    return size + ' ' + unit;
};