JavaScript:
//http://www.kunal-chowdhury.com/2015/12/retrieve-file-size.html
private static string GetFileSize(Uri uriPath)
{
var webRequest = HttpWebRequest.Create(uriPath);
webRequest.Method = "HEAD";
using (var webResponse = webRequest.GetResponse())
{
var fileSize = webResponse.Headers.Get("Content-Length");
var fileSizeInMegaByte = Math.Round(Convert.ToDouble(fileSize) / 1024.0 / 1024.0, 2);
return fileSizeInMegaByte + " MB";
}
}