Dispatcher / Synchronous Events

dispatcher.js

/**
 * Dispatcher
 * 
 * Requires: <script src="http://d3js.org/queue.v1.min.js"></script>
 */
var Dispatcher = function() {
  this._q = queue(1);
  this._events = {};
  this._E = function(message) {
    this.message = message;
    this.name = "DispatcherException";
    this.toString = function() {
      return this.name + ': ' + this.message;
    };
  };
};
Dispatcher.prototype = {
  on: function(event, fn) {
    this._events[event] = this._events[event] || [];
    this._events[event].push(fn);
  },
  off: function(event, fn) {
    if (event in this._events === false) { return; }
    this._events[event].splice(this._events[event].indexOf(fn), 1);
  },
  trigger: function(event /* , args... */) {
    if (event in this._events === false) { return; }

    var ctx = this;
    var args = Array.prototype.slice.call(arguments, 1);
    var tasks = [];
    
    // create an array of tasks out of our event fns for queue
    this._events[event].forEach(function(fn) {
      tasks.push(function(cb) {
        var promise = fn.apply(ctx, args);
        if (promise === undefined) {
          throw new ctx._E('Callback must return a value or a Promise.');
        }
        if (typeof promise.then === 'function') {
          promise.then(
           function(value) { cb(null, value); }, 
           function(value) { cb(value); });
        } else {
          cb(null, promise);
        }
       });
    });
    
    tasks.forEach(function(t) { ctx._q.defer(t); });
    this._q.awaitAll(function(error, results) { console.log("all done!"); });
  }
};

// Example usage:
// 
// var appDispatcher = new Dispatcher();
// 
// appDispatcher.on('change.currentPage', function(name) {
//   appState.currentPage = name;
//   render();
//   return true;
// });