RxJS forkJoin() Join Operator

The RxJS forkJoin() operator is a join operator that accepts an Array of ObservableInput or a dictionary Object of ObservableInput and returns an Observableand then waits for the Observables to complete and then combine last values they emitted.

Syntax:

Following is the syntax of the forkJoin() operator:

Parameter Explanation

value: It specifies a value that input can be an array or dictionary object.

Return value

The forkJoin() operator's return value is an observable that gives the last values emitted from the given observable.

Let us see some examples of forkJoin() operator to understand it clearly.

Example 1

import { of, forkJoin } from 'rxjs';
import { concat } from 'rxjs/operators';
let list1 = of(1, 2, 3, 4, 5);
let list2 = of(6, 7, 8, 9, 10);
let final_val = forkJoin([list1, list2]);
final_val.subscribe(x => console.log(x));

Output:

After executing the above example, you will see the following result:

Here, you can see that it has included the last two values from the both lists in the output.

Similarly, we can apply the RxJS forkJoin() operator for multiple lists. See the following example where we are applying this operator on three lists.

Example 2

import { of, forkJoin } from 'rxjs';
import { concat } from 'rxjs/operators';
let list1 = of(2, 3, 4, 5, 6);
let list2 = of(4, 9, 16, 25, 36);
let list3 = of(20, 60, 80, 90, 100);
let final_val = forkJoin([list1, list2, list3]);
final_val.subscribe(x => console.log(x));

Output:

After executing the above example, you will see the following result:

In the above example, we have applied the forkJoin() operator on 3 lists and you can see that it has included the last values from the all lists in the form of output.

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