while.js

   /**
   *  Repeats source as long as condition holds emulating a while loop.
   * There is an alias for this method called 'whileDo' for browsers <IE9
   *
   * @param {Function} condition The condition which determines if the source will be repeated.
   * @param {Observable} source The observable sequence that will be run if the condition function returns true.
   * @returns {Observable} An observable sequence which is repeated as long as the condition holds.
   */
  var observableWhileDo = Observable['while'] = Observable.whileDo = function (condition, source) {
    isPromise(source) && (source = observableFromPromise(source));
    return enumerableWhile(condition, source).concat();
  };