How to use the @reactivex/rxjs.BehaviorSubject function in @reactivex/rxjs

function DirectLine(options) {
        this.connectionStatus$ = new rxjs_1.BehaviorSubject(BotConnection_1.ConnectionStatus.Uninitialized);
        this.domain = "https://directline.botframework.com/v3/directline";
        this.webSocket = false;
        this.watermark = '';
        this.secret = options.secret;
        this.token = options.secret || options.token;
        if (options.domain)
            this.domain = options.domain;
        if (options.webSocket)
            this.webSocket = options.webSocket;
        this.activity$ = this.webSocket && WebSocket !== undefined
            ? this.webSocketActivity$()
            : this.pollingGetActivity$();
    }
    // Every time we're about to make a Direct Line REST call, we call this first to see check the current connection status.

function DirectLine(secretOrToken, domain) {
        var _this = this;
        if (domain === void 0) { domain = "https://directline.botframework.com"; }
        this.domain = domain;
        this.connected$ = new rxjs_1.BehaviorSubject(false);
        this.token = secretOrToken.secret || secretOrToken.token;
        rxjs_1.Observable.ajax({
            method: "POST",
            url: this.domain + "/api/conversations",
            headers: {
                "Accept": "application/json",
                "Authorization": "BotConnector " + this.token
            }
        })
            .map(function (ajaxResponse) { return ajaxResponse.response; })
            .retryWhen(function (error$) { return error$.delay(1000); })
            .subscribe(function (conversation) {
            _this.conversationId = conversation.conversationId;
            _this.connected$.next(true);
            if (!secretOrToken.secret) {
                rxjs_1.Observable.timer(intervalRefreshToken, intervalRefreshToken).flatMap(function (_) {

createStateStream$(model:IReducer, initialState:T, sideEffects?:SideEffectHandler):Rx.BehaviorSubject {
            const state$ = new Rx.BehaviorSubject(null);
            this.action$
                .startWith(null)
                .scan(
                    (state:T, action:ActionPayload) => {
                        const newState = action !== null ? model.reduce(state, action) : state;
                        sideEffects && action !== null ?
                            sideEffects(newState, action, this.dispatch) :
                            null;
                        return newState;
                    },
                    initialState
                )
                .subscribe(state$);
            return state$;
        }

function DirectLine3(secretOrToken, domain, segment) {
        if (domain === void 0) { domain = "https://directline.botframework.com"; }
        this.domain = domain;
        this.segment = segment;
        this.connected$ = new rxjs_1.BehaviorSubject(false);
        this.secret = secretOrToken.secret;
        this.token = secretOrToken.secret || secretOrToken.token;
    }
    DirectLine3.prototype.start = function () {