text:   /**
     * Returns the first element of an observable sequence that satisfies the condition in the predicate, or a default value if no such element exists.
     * @param {Function} [predicate] A predicate function to evaluate for elements in the source sequence.
     * @param {Any} [defaultValue] The default value if no such element exists.  If not specified, defaults to null.
     * @param {Any} [thisArg] Object to use as `this` when executing the predicate.
     * @returns {Observable} Sequence containing the first element in the observable sequence that satisfies the condition in the predicate, or a default value if no such element exists.
     */
    observableProto.firstOrDefault = function (predicate, defaultValue, thisArg) {
      return predicate ?
        this.where(predicate).firstOrDefault(null, defaultValue) :
        firstOrDefaultAsync(this, true, defaultValue);
    };
  