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

The concat function in the rxjs library is used to merge multiple observables in a sequential manner.

Here's an example of how to use the concat function:

import { of, concat } from 'rxjs';

// create observables
const source1 = of('hello');
const source2 = of('world!');
const source3 = of('rxjs');

// concat the observables
const example = concat(source1, source2, source3);

// subscribe to the concatenated observable
example.subscribe(val => console.log(val));
// output: 'hello', 'world!', 'rxjs'
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In this example, we create three observables using the of function, which emits the values 'hello', 'world!', and 'rxjs' respectively. We then pass these observables as arguments to the concat function to merge them in a sequential manner.

Finally, we subscribe to the concatenated observable and log the emitted values to the console.

Note that the concat function will wait for each observable to complete before moving on to the next one. If an observable never completes, then the concat function will never move on to the next observable.