Observer in JS

beholder.js

/** 
 * Global beholder for communication between blocks.
 *
 * If any callback returns true, next callbacks are NOT executed.
 */
var Beholder = function() {
  var callbacks = {};

  return {
    observe: function(id, callback) {
      if (typeof(callbacks[id]) == 'undefined') {
        callbacks[id] = []
      }
      callbacks[id].push(callback);
    },

    notify: function(id, params) {
      if (typeof(callbacks[id]) != 'undefined') {
        callbacks[id].each(function(callback){
          result = callback.call(this, params);
          if (result === true) {
            throw $break;
          }
        });
      }
    }
  }

}();