subworkers.js

(function(){

  /* Detect if we're in a worker or not */
  var isWorker = false;
  try {
    document;
  } catch (e){
    isWorker = true;
  }

  if (isWorker){
    if (!self.Worker){
      self.Worker = function(path){
        var that = this;
        this.id = Math.random().toString(36).substr(2, 5);

        this.eventListeners = {
          "message": []
        };
        self.addEventListener("message", function(e){
          if (e.data._from === that.id){
            var newEvent = new MessageEvent("message");
            newEvent.initMessageEvent("message", false, false, e.data.message, that, "", null, []);
            that.dispatchEvent(newEvent);
            if (that.onmessage){
              that.onmessage(newEvent);
            }
          }
        });

        var location = self.location.pathname;
        var slashedPath = path.charAt(0) == '/' ? path : '/' + path;
        var absPath = location.substring(0, location.lastIndexOf('/')) + slashedPath;
        self.postMessage({
          _subworker: true,
          cmd: 'newWorker',
          id: this.id,
          path: absPath
        });
      };
      Worker.prototype = {
        onerror: null,
        onmessage: null,
        postMessage: function(message, transfer){
          self.postMessage({
            _subworker: true,
            id: this.id,
            cmd: 'passMessage',
            message: message,
	    transfer: transfer,
          }, transfer);
        },
        terminate: function(){
          self.postMessage({
            _subworker: true,
            cmd: 'terminate',
            id: this.id
          });
        },
        addEventListener: function(type, listener, useCapture){
          if (this.eventListeners[type]){
            this.eventListeners[type].push(listener);
          }
        },
        removeEventListener: function(type, listener, useCapture){
          if (!(type in this.eventListeners)) {
            return;
          }
          var index = this.eventListeners[type].indexOf(listener);
          if (index !== -1){
            this.eventListeners[type].splice(index, 1);
          }
        },
        dispatchEvent: function(event){
          var listeners = this.eventListeners[event.type];
          for (var i = 0; i < listeners.length; i++) {
            listeners[i](event);
          }
        }
      };
    }
  }

  var allWorkers = {};
  var cmds = {
    newWorker: function(event){
      var worker = new Worker(event.data.path);
      worker.addEventListener("message", function(e){
        var envelope = {
          _from: event.data.id,
          message: e.data
        }
        event.target.postMessage(envelope);
      });
      allWorkers[event.data.id] = worker;
    },
    terminate: function(event){
      allWorkers[event.data.id].terminate();
    },
    passMessage: function(event){
      allWorkers[event.data.id].postMessage(event.data.message, event.data.transfer);
    }
  }
  var messageRecieved = function(event){
    if (event.data._subworker){
      cmds[event.data.cmd](event);
    }
  };


  /* Hijack Worker */
  var oldWorker = Worker;
  Worker = function(path){
    if (this.constructor !== Worker){
      throw new TypeError("Failed to construct 'Worker': Please use the 'new' operator, this DOM object constructor cannot be called as a function.");
    }

    var blobIndex = path.indexOf('blob:');
    
    if (blobIndex !== -1 && blobIndex !== 0 ) {
      path = path.substring(blobIndex);
    }

    var newWorker = new oldWorker(path);
    newWorker.addEventListener("message", messageRecieved);

    return newWorker;
  };

})();