src/core/perf/operators/flatmapbase.js

var FlatMapObservable = Rx.FlatMapObservable = (function(__super__) {

    inherits(FlatMapObservable, __super__);

    function FlatMapObservable(source, selector, resultSelector, thisArg) {
      this.resultSelector = isFunction(resultSelector) ? resultSelector : null;
      this.selector = bindCallback(isFunction(selector) ? selector : function() { return selector; }, thisArg, 3);
      this.source = source;
      __super__.call(this);
    }

    FlatMapObservable.prototype.subscribeCore = function(o) {
      return this.source.subscribe(new InnerObserver(o, this.selector, this.resultSelector, this));
    };

    inherits(InnerObserver, AbstractObserver);
    function InnerObserver(observer, selector, resultSelector, source) {
      this.i = 0;
      this.selector = selector;
      this.resultSelector = resultSelector;
      this.source = source;
      this.o = observer;
      AbstractObserver.call(this);
    }

    InnerObserver.prototype._wrapResult = function(result, x, i) {
      return this.resultSelector ?
        result.map(function(y, i2) { return this.resultSelector(x, y, i, i2); }, this) :
        result;
    };

    InnerObserver.prototype.next = function(x) {
      var i = this.i++;
      var result = tryCatch(this.selector)(x, i, this.source);
      if (result === errorObj) { return this.o.onError(result.e); }

      isPromise(result) && (result = observableFromPromise(result));
      (isArrayLike(result) || isIterable(result)) && (result = Observable.from(result));
      this.o.onNext(this._wrapResult(result, x, i));
    };

    InnerObserver.prototype.error = function(e) { this.o.onError(e); };

    InnerObserver.prototype.completed = function() { this.o.onCompleted(); };

    return FlatMapObservable;

}(ObservableBase));