phpjs/workbench/filesystem/file_put_contents.js

php.js offers community built php functions in javascript

function file_put_contents(aFile, data, flags, context) {
  // http://kevin.vanzonneveld.net
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // %          note 1: Only works at present in Mozilla (and unfinished too); might also allow context to determine
  // %          note 1: whether for Mozilla, for HTTP PUT or POST requests, etc.
  // *     example 1: file_put_contents('file://Users/Kevin/someFile.txt', 'hello');
  // *     returns 1: 5


  // Fix: allow file to be placed outside of profile directory; fix: add PHP-style flags, etc.
  var opts = 0, i = 0;

  // Initialize binary arguments. Both the string & integer (constant) input is
  // allowed
  var OPTS = {
    FILE_USE_INCLUDE_PATH: 1,
    LOCK_EX: 2,
    FILE_APPEND: 8,
    FILE_TEXT: 32,
    FILE_BINARY: 64
  };
  if (typeof flags === 'number') {
    opts = flags;
  }
  else { // Allow for a single string or an array of string flags
    flags = [].concat(flags);
    for (i = 0; i < flags.length; i++) {
      if (OPTS[flags[i]]) {
        opts = opts | OPTS[flags[i]];
      } else {

      }
    }
  }
  var append = opts & OPTS.FILE_APPEND;


  var charset = 'UTF-8'; // Can be any character encoding name that Mozilla supports
  // Setting earlier, but even with a different setting, it still seems to save as UTF-8

  //        var em = Cc['@mozilla.org/extensions/manager;1'].
  //                 getService(Ci.nsIExtensionManager);
  //          the path may use forward slash ('/') as the delimiter
  //        var file = em.getInstallLocation(MY_ID).getItemFile(MY_ID, 'content/'+filename);

  var file;
  if ((/^file:\/\//).test(aFile)) {
    // absolute file URL
    var ios = Components.classes['@mozilla.org/network/io-service;1'].
        getService(Components.interfaces.nsIIOService);
    var URL = ios.newURI(aFile, null, null);
    file = URL.QueryInterface(Components.interfaces.nsIFileURL).file; // becomes nsIFile
  }
  else {
    //native

    file = Components.classes['@mozilla.org/file/local;1'].
        createInstance(Components.interfaces.nsILocalFile);
    file.initWithPath(aFile); // e.g., "/home"
  }
  /**
//tmp
var file = Components.classes["@mozilla.org/file/directory_service;1"].
             getService(Components.interfaces.nsIProperties).
             get("TmpD", Components.interfaces.nsIFile);
file.append("suggestedName.tmp");
file.createUnique(Components.interfaces.nsIFile.NORMAL_FILE_TYPE, 438); // 0666
//
var file = Components.classes["@mozilla.org/file/directory_service;1"].
             getService(Components.interfaces.nsIProperties).
             get("ProfD", Components.interfaces.nsIFile);
//*/


  if (typeof file === 'string') {
    var tempfilename = file;
    file = Cc['@mozilla.org/file/directory_service;1'].getService(Ci.nsIProperties).get('ProfD', Ci.nsILocalFile);
    file.append(tempfilename);
  }

  if (!file.exists()) {   // if it doesn't exist, create  // || !file.isDirectory()
    file.create(Ci.nsIFile.NORMAL_FILE_TYPE, 511); // DIRECTORY_TYPE (0777)
  }
  else if (!append) {
    file.remove(false); // I needed to do this to avoid some apparent race condition (the effect of junk getting added to the end)
    file.create(Ci.nsIFile.NORMAL_FILE_TYPE, 511); // DIRECTORY_TYPE (0777)
  }
  // file.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 436); // for temporary (0664)

  var foStream = Cc['@mozilla.org/network/file-output-stream;1'].createInstance(Ci.nsIFileOutputStream);
  var fileFlags = append ? (0x02 | 0x10) : 0x02; // use 0x02 | 0x10 to open file for appending.
  foStream.init(file, fileFlags, 436, 0); // 436 is 0664
  // foStream.init(file, 0x02 | 0x08 | 0x20, 436, 0); // write, create, truncate (436 is 0664)

  var os = Cc['@mozilla.org/intl/converter-output-stream;1'].createInstance(Ci.nsIConverterOutputStream);
  // This assumes that foStream is the nsIOutputStream you want to write to
  // 0x0000 instead of '?' will produce an exception: http://www.xulplanet.com/references/xpcomref/ifaces/nsIConverterOutputStream.html
  // If charset in xsl:output is ISO-8859-1, the file won't open--if it is GB2312, it will output as UTF-8--seems buggy or?
  os.init(foStream, charset, 0, 0x0000);
  os.writeString(data);
  os.close();
  foStream.close();
  // todo: return number of bytes written or false on failure
}