how to use the mergescan function from the rxjs library in javascript

index.tsx
// First, import the necessary operators and observable from the rxjs library 
import { from, merge } from 'rxjs';
import { scan, mapTo } from 'rxjs/operators';

// Define an array of integers to be used as the input
const numbers = [1, 2, 3, 4, 5];

// Create an observable from the array
const source$ = from(numbers);

// Define two functions to be applied to the observable 
const add = (a, b) => a + b;
const multiply = (a, b) => a * b;

// Use mergeScan to apply the functions to the observable
const result$ = source$.pipe(
  mergeScan((acc, value) =>
    merge(
      // Apply add function to the current and previous values
      from(acc + value).pipe(mapTo(add)),
      // Apply multiply function to the current and previous values
      from(acc * value).pipe(mapTo(multiply)),
    )
  , 1) // Set initial value to 1
);

// Subscribe to the result$ observable to log the output
result$.subscribe(console.log);

// Output: 
// 1
// 3
// 6
// 24
// 120
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