export class UiDataService {
    tableDataObs: Observable<TableModel[]>;

    constructor(private httpClient: HttpClient) {
        this.tableDataObs = new Observable<TableModel[]>();
    }

    loadTableData(): Promise<any> {
        return new Promise((resolve, reject) => {
            this.httpClient
                .get('/assets/data/tables.json')
                .map((tables: JSON) => {
                const tableModels: TableModel[] = this.createTableModels(tables);
                this.tableDataObs = of(tableModels); // tableModels has array value here
                // this.tableDataObs.subscribe(s => console.log(s)); again subscribing to observable here returns array
            })
            .subscribe(() => {
                resolve(true);
            });
        });
    }

    getTableModelDataSource(tableName: string): TableModelDataSource {
        this.tableDataObs.subscribe(s => console.log(s)); // this.tableDataObs has nothing to subscribe to here? WHY?
    ...
    }