easy-ngrx-distinct-selector

Provides functions to easily create @ngrx/store selectors with equal functions for arguments and result values.

Motivation 💥

When using @ngrx/store, selectors are often used to transform the state into a more usable form. The default way of creating such selectors is using the createSelector function, which automatically adds the defaultMemoize to the selector to prevent unnecessary recomputations.

If the data structure is a bit more complex one either needs to use the createSelectorFactory to be able to configure the memoize function or the equals (Signals) or distinctUntilChanged (RxJs Observables) functionalities need to be used when the selector is consumed.

The prior makes a lot more sense, as the logic should likely be shared between all consumers of the selector, but it is not as easy to use as the latter.

Features 🔥

✅ Easy to setup and use

✅ Type safe memoize functions

✅ ESM & CJS exports

This library provides a way to easily create selectors with custom memoize functions, which are automatically used when the selector is consumed.

Built With 🔧

• TypeScript

Usage Example 🚀

import { createDistinctSelector } from '@ngneers/easy-ngrx-distinct-selector';

import { AppState } from './app.state';

// By default the selector behaves just like `createSelector`
// Meaning that the memoize functions use the equality operator (===)
const selectBookCount1 = createDistinctSelector(
  (state: AppState) => state.book,
  book => book.count
);

// With custom result equality function
const selectBookNames = createDistinctSelector(
  (state: AppState) => state.book,
  book => book.names,
  { resultEqual: (oldNames, newNames) => arraysEqual(oldNames, newNames) }
);

// With custom arguments equality function
// `argsEqual` is different than `defaultMemoize` as it is only called once
// per selector call with all arguments instead of once per argument to improve type safety
const selectFilteredBookNames1 = createDistinctSelector(
  (state: AppState) => state.book.names,
  (state: AppState) => state.book.filter,
  (names, filter) => names.filter(name => name.includes(filter)),
  {
    argsEqual: ([oldNames, oldFilter], [newNames, newFilter]) => {
      return arraysEqual(oldNames, newNames) && oldFilter === newFilter;
    },
  }
);

// Parameterized selectors are also supported
function selectFilteredBookNames2(props: { filter: string }) {
  return createDistinctSelector(
    (state: AppState) => state.book.names,
    names => names.filter(name => name.includes(props.filter)),
    {
      argsEqual: ([oldNames], [newNames]) => {
        return arraysEqual(oldNames, newNames);
      },
    }
  );
}

// Unlike `createSelector `, `createDistinctSelector` also accepts direct projection of the state
const selectBookCount2 = createDistinctSelector((state: AppState) => state.book.count);

// ... that also supports custom memoize functions
const selectBookCount3 = createDistinctSelector((state: AppState) => state.book.count, {
  argsEqual: ([oldState], [newState]) => oldState.book.count === newState.book.count,
});

// Utility functions for selectors
function arraysEqual<T>(oldArray: T[], newArray: T[]): boolean {
  return (
    oldArray.length !== newArray.length &&
    oldArray.every((value, index) => value === newArray[index])
  );
}

Contributing 🧑🏻‍💻

Contributions are what make the open source community such an amazing place to learn, inspire, and create. Any contributions you make are greatly appreciated.

If you have a suggestion that would make this better, please fork the repo and create a pull request. You can also simply open an issue with the tag "enhancement". Don't forget to give the project a star! Thanks again!

1. Fork the Project
2. Create your Feature Branch (git checkout -b feature/AmazingFeature)
3. Commit your Changes (git commit -m 'Add some AmazingFeature')
4. Push to the Branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

License 🔑

Distributed under the MIT License. See LICENSE.txt for more information.