Tiny javascript observable

gistfile1.txt

function observable(obj) {
  var listeners = {};
  //
  obj.on = function(name, handler) {
    if (! (name in listeners)) {
      listeners[name] = [];
    }
    listeners[name].push(handler);
    return this;
  };
  //
  obj.off = function(name, handler) {
    if (! handler && name in listeners) {
      delete listeners[name];
      return this;
    }
    for (var i=0,ln=listeners[name].length; i<ln; i++) {
      if (listeners[name][i] === handler) {
        listeners[name][i].splice(i, 1);
      }
    }
    return this;
  };
  //
  obj.trigger = function(name, params) {
    if (! (name in listeners)) {
      return this;
    }
    for (var i=0,ln=listeners[name].length; i<ln; i++) {
      listeners[name][i].apply(obj, params);
    }
    return this;
  };
  return obj;
}