app/static/recorder.js

(function(window){

  var WORKER_PATH = '/static/recorderWorker.js';

  var Recorder = function(source, cfg){
    var config = cfg || {};
    var bufferLen = config.bufferLen || 4096;
    this.context = source.context;
    if(!this.context.createScriptProcessor){
       this.node = this.context.createJavaScriptNode(bufferLen, 2, 2);
    } else {
       this.node = this.context.createScriptProcessor(bufferLen, 2, 2);
    }
   
    var worker = new Worker(config.workerPath || WORKER_PATH);
    worker.postMessage({
      command: 'init',
      config: {
        sampleRate: this.context.sampleRate
      }
    });
    var recording = false,
      currCallback;

    this.node.onaudioprocess = function(e){
      if (!recording) return;
      worker.postMessage({
        command: 'record',
        buffer: [
          e.inputBuffer.getChannelData(0),
          e.inputBuffer.getChannelData(1)
        ]
      });
    }

    this.configure = function(cfg){
      for (var prop in cfg){
        if (cfg.hasOwnProperty(prop)){
          config[prop] = cfg[prop];
        }
      }
    }

    this.record = function(){
      recording = true;
    }

    this.stop = function(){
      recording = false;
    }

    this.clear = function(){
      worker.postMessage({ command: 'clear' });
    }

    this.getBuffers = function(cb) {
      currCallback = cb || config.callback;
      worker.postMessage({ command: 'getBuffers' })
    }

    this.exportWAV = function(cb, type){
      currCallback = cb || config.callback;
      type = type || config.type || 'audio/wav';
      if (!currCallback) throw new Error('Callback not set');
      worker.postMessage({
        command: 'exportWAV',
        type: type
      });
    }

    this.exportMonoWAV = function(cb, type){
      currCallback = cb || config.callback;
      type = type || config.type || 'audio/wav';
      if (!currCallback) throw new Error('Callback not set');
      worker.postMessage({
        command: 'exportMonoWAV',
        type: type
      });
    }

    worker.onmessage = function(e){
      var blob = e.data;
      currCallback(blob);
    }

    source.connect(this.node);
    this.node.connect(this.context.destination);   // if the script node is not connected to an output the "onaudioprocess" event is not triggered in chrome.
  };

  Recorder.setupDownload = function(blob, filename){
    var url = (window.URL || window.webkitURL).createObjectURL(blob);
    var link = document.getElementById("save");
    link.href = url;
    link.download = filename || 'output.wav';
  }

  window.Recorder = Recorder;

})(window);