Merge Latest From Operator to get latest emission of other source observables

merge latest from.ts

export type ObservableSourceType<T = any> = Observable<T> | ((value: any) => Observable<T>);

function* sourcesGen<T>(sources: ObservableSourceType[], a: T, i: number): Generator<Observable<any>, Observable<any>, undefined> {
  const length = sources.length;
  for (const [index, source] of sources.entries()) {
    const observableSource: Observable<any> = typeof source === 'function' ? source.call(null, [a, i]) : source;
    if (index <= length + 1) {
      yield observableSource;
    } else {
      return observableSource;
    }
  }
}

export function mergeLatestFrom<T>(...inputs: any[]): OperatorFunction<T, any[]> {
  let concurrency: number;
  if (typeof inputs[inputs.length - 1] === 'number') {
    concurrency = inputs.pop();
  }

  const sources: ObservableSourceType[] = inputs;

  return (source: Observable<T>) =>
    source.pipe(mergeMap((a, i) => of(a).pipe(withLatestFrom<T, any[]>(...sourcesGen(sources, a, i))), concurrency));
}