tomap.js

  /**
   * Converts the observable sequence to a WeakMap if it exists.
   * @param {Function} keySelector A function which produces the key for the WeakMap
   * @param {Function} [elementSelector] An optional function which produces the element for the WeakMap. If not present, defaults to the value from the observable sequence.
   * @returns {Observable} An observable sequence with a single value of a WeakMap containing the values from the observable sequence.
   */
  function toMap(source, type, keySelector, elementSelector) {
    return new AnonymousObservable(function (observer) {
      var m = new type();
      return self.subscribe(
        function (x) {
          var key;
          try {
            key = keySelector(x);
          } catch (e) {
            observer.onError(e);
            return;
          }

          var element = x;
          if (elementSelector) {
            try {
              element = elementSelector(x);
            } catch (e) {
              observer.onError(e);
              return;
            }              
          }

          m.set(key, element);
        },
        observer.onError.bind(observer),
        function () {
          observer.onNext(m);
          observer.onCompleted();
        })
    });
  }
  
  if (!!window.Map) {
    Rx.Observable.prototype.toMap = function (keySelector, elementSelector) {
      return toMap(this, window.Map, keySelector, elementSelector);  
    }
  }
  
  if (!!window.WeakMap) {
    Rx.Observable.prototype.toWeakMap = function (keySelector, elementSelector) {
      return toMap(this, window.WeakMap, keySelector, elementSelector);  
    }
  }