jscodeshift-rxjs-first-value-from

This codemod automates the migration from RxJS’s deprecated .toPromise() method to firstValueFrom and lastValueFrom. Promises piped with take(1) or first() are replaced with firstValueFrom, while other cases default to lastValueFrom. Import statements are also updated to include the new functions and remove unused imports.

• jscodeshift-rxjs-first-value-from
  • Installation
  • Usage
    • Options
    • Examples
      • toPromise to firstValueFrom
      • toPromise to lastValueFrom
      • toPromise with type argument
      • subscribe to firstValueFrom
  • Running Unit Tests
  • Contributing
  • License

Installation

To install the codemod, you can use npm or yarn.

npm install --save-dev jscodeshift-rxjs-first-value-from
# or
yarn add --dev jscodeshift-rxjs-first-value-from

You'll also need jscodeshift, the framework that powers this codemod.

npm install -g jscodeshift

Usage

To run the codemod, use the jscodeshift CLI and specify the path to the files you want to transform.

jscodeshift -t ./node_modules/jscodeshift-rxjs-first-value-from/src/first-value-from.ts src

Options

You can pass options to the codemod via jscodeshift if needed. This example is minimal in options, but you can extend or customize the script based on your project requirements.

Examples

toPromise to firstValueFrom

When calling toPromise on a pipe containing take(1) or first() the codemod will replace it with firstValueFrom.

Before:

import { take, map } from "rxjs/operators";

const name = getUser().pipe(map((user) => user.name), take(1)).toPromise();

After running the codemod:

import { firstValueFrom } from "rxjs";
import { map } from "rxjs/operators";

const name = firstValueFrom(getUser().pipe(map((user) => user.name)));

toPromise to lastValueFrom

When calling toPromise on a pipe without take(1) or first() the codemod will replace it with lastValueFrom.

Before:

import { map } from "rxjs/operators";

const name = getUser().pipe(map((user) => user.name)).toPromise();

After running the codemod:

import { lastValueFrom } from "rxjs";
import { map } from "rxjs/operators";

const name = lastValueFrom(getUser().pipe(map((user) => user.name)));

toPromise with type argument

When calling toPromise with a type argument, the codemod will cast the observable to the specified type.

Before:

import { map } from "rxjs/operators";

const name = getUser().pipe(map((user) => user.name)).toPromise<string>();

After running the codemod:

import { lastValueFrom } from "rxjs";
import { map } from "rxjs/operators";

const name = lastValueFrom(getUser().pipe(map((user) => user.name)) as Observable<string>);

subscribe to firstValueFrom

When calling subscribe on an observable with a single value, the codemod will replace it with firstValueFrom.

Before:

import { map } from "rxjs/operators";

getUser().pipe(map((user) => user.name), take(1)).subscribe((name) => console.log(name));

After running the codemod:

import { firstValueFrom } from "rxjs";
import { map } from "rxjs/operators";

firstValueFrom(getUser().pipe(map((user) => user.name))).then((name) => console.log(name));

Running Unit Tests

This repository includes a suite of unit tests to ensure the codemod behaves as expected across a variety of cases.

To run the tests, install the dependencies and use vitest:

npm install
npm test

Contributing

Contributions are welcome! If you’d like to contribute, please fork the repository and submit a pull request.

1. Fork the project
2. Create a feature branch (git checkout -b feature-name)
3. Commit your changes (git commit -m 'Add some feature')
4. Push to the branch (git push origin feature-name)
5. Open a pull request

Please make sure to update tests as appropriate.

License

This project is licensed under the MIT License - see the LICENSE file for details.