diff --git a/nrtsc140.js b/nrtsc140.js
index 0ade848..767b73a 100644
--- a/nrtsc140.js
+++ b/nrtsc140.js
@@ -1,10 +1,10 @@
 /**
  * Constants.
  */
-const MAX_RECORDING_SEC = 30;
-const SC_SEVER_STARTED_MSG = 'notification is on';
-const SC_SEVER_START_ERR_MSG = 'server failed to start';
-const JACK_DRIVER_IGNORE_MSG = 'JackDriver: max output latency';
+var MAX_RECORDING_SEC = 30;
+var SC_SEVER_STARTED_MSG = 'notification is on';
+var SC_SEVER_START_ERR_MSG = 'server failed to start';
+var JACK_DRIVER_IGNORE_MSG = 'JackDriver: max output latency';
 
 /**
  * Module dependencies.
@@ -17,102 +17,88 @@ var sio = require('socket.io')
   , util = require('util')
 
 var NrtSc140 = exports.NrtSc140 = function(socket) {
-  var _socket = socket;
-  var _audioDir = path.join(process.cwd(), 'public', 'audio');
-  var _curFile = null;
-  var _generatedFiles = new Array();
-  var _timeoutId = null;
-  var _intervalId = null;
-  var _sclang = null;
-  var _sclangStdoutHandler = function(data) {
-    util.debug('sclang stdout: ' + data);
-    var msg = '' + data;
-    if (msg.indexOf(SC_SEVER_STARTED_MSG) != -1) {
-      _socket.emit('scserverstarted');
-    } else if (msg.indexOf(SC_SEVER_START_ERR_MSG) != -1) {
-    } else if (msg.indexOf(JACK_DRIVER_IGNORE_MSG) != -1) {
-      // FIXME workaround
-      // in case other user start sclang
-      return; // ignore
-    }
-    _socket.emit('stdout', msg);
-  };
-  
-  NrtSc140.prototype.start = function() {
-    _socket.emit('scserverstarting');
-    _sclang = createSclang(_sclangStdoutHandler, _generatedFiles);
-    _socket.on('validate', this.onValidate);
-    _socket.on('generate', this.onGenerate);
-    _socket.on('stop', this.onStop);
-    _socket.on('restartsclang', this.onRestartSclang);
-    _socket.on('disconnect', this.onSocketDisconnect);
-  }
-    
-  NrtSc140.prototype.onRestartSclang = function() {
-    _socket.emit('scserverstarting');
-    _sclang.dispose();
-    _sclang = createSclang(_sclangStdoutHandler, _generatedFiles);
-  }
-  
-  NrtSc140.prototype.onValidate = function(msg) {
-    util.debug('validate: ' + msg);
-    validateScCode(msg, _socket);
-  }
+  this._socket = socket;
+  this._audioDir = path.join(process.cwd(), 'public', 'audio');
+  this._curFile = null;
+  this._generatedFiles = new Array();
+  this._timeoutId = null;
+  this._intervalId = null;
+  this._sclang = null;
+};
+
+NrtSc140.prototype.start = function() {
+  this._socket.emit('scserverstarting');
+  this._sclang = this.createSclang();
+  this._socket.on('validate', this.onValidate.bind(this));
+  this._socket.on('generate', this.onGenerate.bind(this));
+  this._socket.on('stop', this.onStop.bind(this));
+  this._socket.on('restartsclang', this.onRestartSclang.bind(this));
+  this._socket.on('disconnect', this.onSocketDisconnect.bind(this));
+}
 
-  NrtSc140.prototype.onGenerate = function(msg) {
-    util.debug('generate: ' + msg);
-    if (!validateScCode(msg, _socket)) return;
-
-    var aiffFile;
-    do {
-      _curFile = randomString();
-      aiffFile = path.join(_audioDir, _curFile + '.aiff');
-      util.debug('aiffFile: ' + aiffFile);
-    } while (path.existsSync(aiffFile));
-    //_generatedFiles.push(path.join(_audioDir, _curFile + '.*'));
-    _sclang.evaluate(
-      's.waitForBoot(s.prepareForRecord(\'' 
-      + aiffFile + '\');s.record;' 
-      + msg + '\n);', false);
-
-    var timeRemaining = MAX_RECORDING_SEC + 1;
-    _timeoutId = setTimeout(function() {
-      _timeoutId = stopRecording(_sclang, _socket, _audioDir, _curFile);
-    }, timeRemaining * 1000);
-
-    var timeRecorded = 0;
+NrtSc140.prototype.onRestartSclang = function() {
+  this._socket.emit('scserverstarting');
+  if (this._sclang) this._sclang.dispose();
+  this._sclang = this.createSclang();
+}
+
+NrtSc140.prototype.onValidate = function(msg) {
+  util.debug('validate: ' + msg);
+  this.validateScCode(msg, this._socket);
+}
+
+NrtSc140.prototype.onGenerate = function(msg) {
+  util.debug('generate: ' + msg);
+  if (!this.validateScCode(msg, this._socket)) return;
+
+  var aiffFile;
+  do {
+    this._curFile = randomString();
+    aiffFile = path.join(this._audioDir, this._curFile + '.aiff');
+    util.debug('aiffFile: ' + aiffFile);
+  } while (path.existsSync(aiffFile));
+  //this._generatedFiles.push(path.join(_audioDir, _curFile + '.*'));
+  this._sclang.evaluate(
+    's.waitForBoot(s.prepareForRecord(\'' 
+    + aiffFile + '\');s.record;' 
+    + msg + '\n);', false);
+
+  var timeRemaining = MAX_RECORDING_SEC + 1;
+  this._timeoutId = setTimeout(function() {
+    this._timeoutId = this.stopRecording();
+  }.bind(this), timeRemaining * 1000);
+
+  var timeRecorded = 0;
+  util.debug('timerecorded: ' + timeRecorded);
+  this._socket.emit('timerecorded', '' + timeRecorded);
+  this._intervalId = setInterval(function() {
+    timeRecorded++;
     util.debug('timerecorded: ' + timeRecorded);
-    _socket.emit('timerecorded', '' + timeRecorded);
-    _intervalId = setInterval(function() {
-      timeRecorded++;
-      util.debug('timerecorded: ' + timeRecorded);
-      _socket.emit('timerecorded', '' + timeRecorded);
-      if (timeRecorded >= MAX_RECORDING_SEC) clearInterval(_intervalId);
-    }, 1000);
-  };
-
-  NrtSc140.prototype.onStop = function() {
-    util.debug('stop');
-    if (_timeoutId) clearTimeout(_timeoutId);
-    if (_intervalId) clearInterval(_intervalId);
-    _timeoutId = stopRecording(_sclang, _socket, _audioDir, _curFile);
-  }
+    this._socket.emit('timerecorded', '' + timeRecorded);
+    if (timeRecorded >= MAX_RECORDING_SEC) clearInterval(this._intervalId);
+  }.bind(this), 1000);
+};
 
-  NrtSc140.prototype.onSocketDisconnect = function() {
-    util.debug('disconnect');
-    if (_timeoutId) clearTimeout(_timeoutId);
-    if (_intervalId) clearInterval(_intervalId);
-    
-    _sclang.dispose();
-    
-    for (i in _generatedFiles) {
-      rmFile(_generatedFiles[i]);
-    }
+NrtSc140.prototype.onStop = function() {
+  util.debug('stop');
+  if (this._timeoutId) clearTimeout(this._timeoutId);
+  if (this._intervalId) clearInterval(this._intervalId);
+  this._timeoutId = this.stopRecording();
+}
+
+NrtSc140.prototype.onSocketDisconnect = function() {
+  util.debug('disconnect');
+  if (this._timeoutId) clearTimeout(this._timeoutId);
+  if (this._intervalId) clearInterval(this._intervalId);
+  if (this._sclang) this._sclang.dispose();
+  for (var i in this._generatedFiles) {
+    rmFile(this._generatedFiles[i]);
   }
-};
+}
 
-function createSclang(handler, generatedFiles) {
-  var sclang = new sc.Sclang('/usr/bin/', handler);
+NrtSc140.prototype.createSclang = function() {
+  var sclang = 
+    new sc.Sclang('/usr/bin/', this.onSclangStdoutReceived.bind(this));
   sclang.evaluate('Server.default = Server.internal;s = Server.default;s.boot;');
 
   // FIXME workaround
@@ -120,7 +106,7 @@ function createSclang(handler, generatedFiles) {
   do {
     workaroundTmpFile = '/tmp/nrt-sc140-' + randomString() + '.aiff';
   } while (path.existsSync(workaroundTmpFile));
-  generatedFiles.push(workaroundTmpFile);
+  this._generatedFiles.push(workaroundTmpFile);
   sclang.evaluate(
     's.waitForBoot(s.prepareForRecord(\'' 
     + workaroundTmpFile
@@ -129,39 +115,52 @@ function createSclang(handler, generatedFiles) {
   return sclang;
 }
 
-function validateScCode(msg, socket) {
-    if (msg.length < 1) {
-      socket.emit('validationerror', 'code can not be blank.');
-      return false;
-    }
-    if (msg.length > 140) {
-      socket.emit('validationerror', 'code can not be over 140.');
-      return false;
-    }
-    if (msg.indexOf('unixCmd') != -1) {
-      socket.emit('validationerror', '\'unixCmd\' can not be executed.');
-      return false;
-    }
-    socket.emit('validationerror', '');
-    return true;
+NrtSc140.prototype.onSclangStdoutReceived = function(data) {
+  util.debug('sclang stdout: ' + data);
+  var msg = '' + data;
+  if (msg.indexOf(SC_SEVER_STARTED_MSG) != -1) {
+    this._socket.emit('scserverstarted');
+  } else if (msg.indexOf(SC_SEVER_START_ERR_MSG) != -1) {
+  } else if (msg.indexOf(JACK_DRIVER_IGNORE_MSG) != -1) {
+    // FIXME workaround
+    // in case other user start sclang
+    return; // ignore
+  }
+  this._socket.emit('stdout', msg);
+}
+
+NrtSc140.prototype.validateScCode = function(msg) {
+  if (msg.length < 1) {
+    this._socket.emit('validationerror', 'code can not be blank.');
+    return false;
+  }
+  if (msg.length > 140) {
+    this._socket.emit('validationerror', 'code can not be over 140.');
+    return false;
+  }
+  if (msg.indexOf('unixCmd') != -1) {
+    this._socket.emit('validationerror', '\'unixCmd\' can not be executed.');
+    return false;
+  }
+  this._socket.emit('validationerror', '');
+  return true;
 }
 
-function stopRecording(sclang, socket, audioDir, filename) {
-  sclang.evaluate('s.stopRecording;', false);
-  sclang.stopSound();
-  var timeoutId = setTimeout(function() {
-    var aiffFile = path.join(audioDir, filename + '.aiff');
-    var mp3File = path.join(audioDir, filename + '.mp3');
+NrtSc140.prototype.stopRecording = function() {
+  this._sclang.evaluate('s.stopRecording;', false);
+  this._sclang.stopSound();
+  this._timeoutId = setTimeout(function() {
+    var aiffFile = path.join(this._audioDir, this._curFile + '.aiff');
+    var mp3File = path.join(this._audioDir, this._curFile + '.mp3');
     convert(aiffFile, mp3File, function(error, stdout, stderr) {
       util.debug('stdout: ' + stdout);
       util.debug('stderr: ' + stderr);
       if (error != null) {
         util.debug('exec error: ' + error);
       }
-      socket.emit('filegenerated', filename);
-    });
-  }, 1000);
-  return timeoutId;
+      this._socket.emit('filegenerated', this._curFile);
+    }.bind(this));
+  }.bind(this), 1000);
 }
 
 function randomString() {