Method observe

src/cdk/layout/breakpoints-observer.ts:74–97

* Gets an observable of results for the given queries that will emit new results for any changes * in matching of the given queries. * @param value One or more media queries to check. * @returns A stream of matches for the given queries.

(value: string | readonly string[])

   * @returns A stream of matches for the given queries.
   */
  observe(value: string | readonly string[]): Observable<BreakpointState> {
    const queries = splitQueries(coerceArray(value));
    const observables = queries.map(query => this._registerQuery(query).observable);

    let stateObservable = combineLatest(observables);
    // Emit the first state immediately, and then debounce the subsequent emissions.
    stateObservable = concat(
      stateObservable.pipe(take(1)),
      stateObservable.pipe(skip(1), debounceTime(0)),
    );
    return stateObservable.pipe(
      map(breakpointStates => {
        const response: BreakpointState = {
          matches: false,
          breakpoints: {},
        };
        breakpointStates.forEach(({matches, query}) => {
          response.matches = response.matches || matches;
          response.breakpoints[query] = matches;
        });
        return response;
      }),
    );
  }

  /** Registers a specific query to be listened for. */
  private _registerQuery(query: string): Query {