Rxjs vs Lodash ? can rxjs be an alternative for lodash?

It depends on what you do. Some tasks can be achieved by both, but many tasks can only be achieved by one of the two. RxJS is not an alternative to Lodash.

Note that they have completely different missions:

• Lodash makes JavaScript easier by taking the hassle out of working with arrays, numbers, objects, strings, etc.
• RxJS is a library for reactive programming using Observables, to make it easier to compose asynchronous or callback-based code.

They are completely different things. But i do understand the confusion: they look comparable, but what to do is very different.

Lodash: can be compared to Linq in .Net. Its all about navigating, combining and manipulating lists or enumerable things.

Rxjs: is not about lists, but about events that happen over time.

It actually makes sense to use them both:

// every time filter criteria is updated on the GUI, this will emit a new set of filtercriteria
let filterCriteria$ = new BehaviorSubject<FilterCriteria>({});
// this gets the list of employees, but will also emit a new set of employees when there are any changes
let mostRecentListOfEmployees$: Observable<Employee[]> = this.apiService.GetEmployees();

// using combineLatest will make sure that the map operator is executed every time the criteria or the list is updated
let filteredEmployees$ = filterCriteria$.pipe(
    combineLatest(mostRecentListOfEmployees$),
    map(([filterCriteria, list]) => {
        // this is pseudocode, not sure about the exact lodash syntax for filtering ...
        return _.filter(list, filterCriteria);
    })
)

You would rely on Rxjs to refilter the list every time the filter criteria is updated, and when a new set of employees comes in via the api.

Lodash would be used to do the actual filtering on the array.

Your GUI would subscribe to the filteredEmployees$ observable.

If this approach seems unfamiliar, this is whats called Reactive Programming: https://en.wikipedia.org/wiki/Reactive_programming

They are both completely different things. RxJS Uses the concept of reactive programming. Using the Observable and observer pattern you are able to create streams of data (A Pipeline in between) where you are able to use RxJS's operators to do work on the data. These operators do one thing that Lodash does not which is very specific to RxJS. The operators return observables allowing you to properly chain other RxJS Observable operators to the result of the first.

I have not used lodash very much but i'm assuming it does not return an observable as it is made specifically to work with arrays. I have used it a bit and it works great to add functionality to modifying arrays but I am assuming it would not help the data stream/pipeline operations which RxJS uses.