Adding JavaScript for enabling file sharing

First, we add a new global variable that is used to hold all the data that defines the list of files that have been shared.

var file_store = []; // shared file storage

Then, at the end of the start() function, we add an if/else block, which detects if our browser supports all of the capabilities required to enable file sharing.

  // setup file sharing
  if (!(window.File
        && window.FileReader
        && window.FileList
        && window.Blob)) {
    document.getElementById("file_sharing").style.display = "none";
    alert("This browser does not support File Sharing");
  } else {
    document.getElementById("file_add").onclick = click_file_input;
    document.getElementById("file_input").addEventListener("change",file_input, false);
    document.getElementById("open_call_state").addEventListener("dragover", drag_over, false);
    document.getElementById("open_call_state").addEventListener("drop", file_input, false);
...