recorder.js

(function (window) {

  var Recorder = function (source, cfg) {
    var config = cfg || {};
    var bufferLen = config.bufferLen || 4096;
    var numChannels = config.numChannels || 2;

    this.context = source.context;
    this.node = (this.context.createScriptProcessor || this.context.createJavaScriptNode)
      .call(this.context, bufferLen, numChannels, numChannels);

    var recording = false,
      currCallback;
    var worker = new Worker(config.workerPath || 'recorderWorker.js');
    worker.postMessage({
      command: 'init',
      config: {
        sampleRate: this.context.sampleRate,
        numChannels: numChannels
      }
    });

    this.node.onaudioprocess = function (e) {
      if (!recording) return;
      var buffer = [];
      for (var channel = 0; channel < numChannels; channel++) {
        buffer.push(e.inputBuffer.getChannelData(channel));
      }
      worker.postMessage({
        command: 'record',
        buffer: buffer
      });
    };

    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.getBuffer = function (cb) {
      currCallback = cb;
      worker.postMessage({ command: 'getBuffer' })
    };

    this.exportWAV = function (cb) {
      this.exportCustomWAV(null, cb);
    };

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

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

    source.connect(this.node);
    this.node.connect(this.context.destination);    //this should not be necessary
  };

  Recorder.forceDownload = function (blob, filename) {
    var url = (window.URL || window.webkitURL).createObjectURL(blob);
    var link = window.document.createElement('a');
    link.href = url;
    link.download = filename || 'output.wav';
    var click = document.createEvent("Event");
    click.initEvent("click", true, true);
    link.dispatchEvent(click);
  };

  window.Recorder = Recorder;

})(window);