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

To use the firstValueFrom() function from RxJS library, first, we need to create an Observable in our JavaScript code. We can do so using the from() function provided by RxJS.

import { from } from 'rxjs';

const observableData = from([1, 2, 3, 4, 5]);

// Using firstValueFrom() function
firstValueFrom(observableData).then((value) => console.log(value));
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In the above example, we have created an Observable observableData which emits an array of numbers. We then use the firstValueFrom() function to get the first value emitted by the Observable. We pass our Observable observableData as a parameter to the firstValueFrom() function.

The firstValueFrom() function returns a Promise which we can use to access the first emitted value. In the above example, we have used the .then() method to log the first value to the console.

Note: firstValueFrom() function is part of the ES2017 JavaScript standard, but it is implemented in RxJS version 6.5 or later. If you are using an older version of RxJS, you can use the toPromise() method to convert the Observable to a Promise and then use the native JavaScript Promise function then() as follows:

observableData.toPromise().then((value) => console.log(value));
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But it is recommended to use firstValueFrom() function as it provides better error handling and is more efficient.