from.js

  var FromObservable = (function(__super__) {
    inherits(FromObservable, __super__);
    function FromObservable(iterable, fn, scheduler) {
      this._iterable = iterable;
      this._fn = fn;
      this._scheduler = scheduler;
      __super__.call(this);
    }

    function createScheduleMethod(o, it, fn) {
      return function loopRecursive(i, recurse) {
        var next = tryCatch(it.next).call(it);
        if (next === errorObj) { return o.onError(next.e); }
        if (next.done) { return o.onCompleted(); }

        var result = next.value;

        if (isFunction(fn)) {
          result = tryCatch(fn)(result, i);
          if (result === errorObj) { return o.onError(result.e); }
        }

        o.onNext(result);
        recurse(i + 1);
      };
    }

    FromObservable.prototype.subscribeCore = function (o) {
      var list = Object(this._iterable),
          it = getIterable(list);

      return this._scheduler.scheduleRecursive(0, createScheduleMethod(o, it, this._fn));
    };

    return FromObservable;
  }(ObservableBase));

  var maxSafeInteger = Math.pow(2, 53) - 1;

  function StringIterable(s) {
    this._s = s;
  }

  StringIterable.prototype[$iterator$] = function () {
    return new StringIterator(this._s);
  };

  function StringIterator(s) {
    this._s = s;
    this._l = s.length;
    this._i = 0;
  }

  StringIterator.prototype[$iterator$] = function () {
    return this;
  };

  StringIterator.prototype.next = function () {
    return this._i < this._l ? { done: false, value: this._s.charAt(this._i++) } : doneEnumerator;
  };

  function ArrayIterable(a) {
    this._a = a;
  }

  ArrayIterable.prototype[$iterator$] = function () {
    return new ArrayIterator(this._a);
  };

  function ArrayIterator(a) {
    this._a = a;
    this._l = toLength(a);
    this._i = 0;
  }

  ArrayIterator.prototype[$iterator$] = function () {
    return this;
  };

  ArrayIterator.prototype.next = function () {
    return this._i < this._l ? { done: false, value: this._a[this._i++] } : doneEnumerator;
  };

  function numberIsFinite(value) {
    return typeof value === 'number' && root.isFinite(value);
  }

  function isNan(n) {
    return n !== n;
  }

  function getIterable(o) {
    var i = o[$iterator$], it;
    if (!i && typeof o === 'string') {
      it = new StringIterable(o);
      return it[$iterator$]();
    }
    if (!i && o.length !== undefined) {
      it = new ArrayIterable(o);
      return it[$iterator$]();
    }
    if (!i) { throw new TypeError('Object is not iterable'); }
    return o[$iterator$]();
  }

  function sign(value) {
    var number = +value;
    if (number === 0) { return number; }
    if (isNaN(number)) { return number; }
    return number < 0 ? -1 : 1;
  }

  function toLength(o) {
    var len = +o.length;
    if (isNaN(len)) { return 0; }
    if (len === 0 || !numberIsFinite(len)) { return len; }
    len = sign(len) * Math.floor(Math.abs(len));
    if (len <= 0) { return 0; }
    if (len > maxSafeInteger) { return maxSafeInteger; }
    return len;
  }

  /**
  * This method creates a new Observable sequence from an array-like or iterable object.
  * @param {Any} arrayLike An array-like or iterable object to convert to an Observable sequence.
  * @param {Function} [mapFn] Map function to call on every element of the array.
  * @param {Any} [thisArg] The context to use calling the mapFn if provided.
  * @param {Scheduler} [scheduler] Optional scheduler to use for scheduling.  If not provided, defaults to Scheduler.currentThread.
  */
  var observableFrom = Observable.from = function (iterable, mapFn, thisArg, scheduler) {
    if (iterable == null) {
      throw new Error('iterable cannot be null.')
    }
    if (mapFn && !isFunction(mapFn)) {
      throw new Error('mapFn when provided must be a function');
    }
    if (mapFn) {
      var mapper = bindCallback(mapFn, thisArg, 2);
    }
    isScheduler(scheduler) || (scheduler = currentThreadScheduler);
    return new FromObservable(iterable, mapper, scheduler);
  }