XPCOM File I/O

xpcom_file_io.js

const {classes: Cc, interfaces: Ci, utils: Cu} = Components;
Cu.import("resource://gre/modules/NetUtil.jsm");

// Let's enumerate all available files in ~
function getHomeDir() {
  let home = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsILocalFile);
  home.initWithPath("~");

  if (!home.isDirectory()) {
    alert("that seems wrong...");
    return;
  }

  return home.directoryEntries;
}

// Read a text/plain file into a string
function readFile(file, cb) {
  alert("reading " + file.path);
  
  let channel = NetUtil.newChannel(file);
  channel.contentType = "text/plain";
  
  NetUtil.asyncFetch(file, function(is, result) {
    if (!Components.isSuccessCode(status)) {
      cb("error while reading...");
      return;
    }
    let data =
      NetUtil.readInputStreamToString(is, is.available());
    is.close();
    cb(data);
  });
}

// Opening and reading the first file in ~
let files = [];
let homedir = getHomeDir();
while (homedir.hasMoreElements()) {
  let file = homedir.getNext().QueryInterface(Ci.nsIFile);
  if (!file.isDirectory()) {
    files.push(file);
  }
}

readFile(files[0], function(a) { alert(a); } );