5 Tips for Angular Developers Using RxJS for State Management

Being an Angular developer, you must be aware of RxJS, an incredibly powerful reactive programming library. RxJS plays a key role in building scalable Angular applications. When it comes to state management in Angular, RxJS is an excellent choice. With RxJS, you can handle complex state scenarios without using complex logic.

But, using RxJS for state management can be challenging, especially for developers who are just starting their Angular journey. In this article, we’ll share five tips to make it easier for you to use RxJS for state management in Angular.

Tip #1 - Use Behavior Subjects to Initialize State

When using RxJS for state management in Angular, initializing the state can be a tricky task. But this can be solved by using Behavior Subjects. A Behavior Subject is like an Observable, but with an initial value. When an Observer subscribes to a Behavior Subject, it instantly emits the most recent value that its subject emitted.

For example:

import { BehaviorSubject } from 'rxjs';

const initialState = {
  name: '',
  age: null,
};

const state$ = new BehaviorSubject(initialState);

Here, we’ve created a Behavior Subject and initialized its value with an object containing name and age properties.

You can update the state with the next() method of the Behavior Subject, as shown below:

state$.next({
  name: 'John Doe',
  age: 30,
});

Using Behavior Subjects for initializing state can make your code simpler and easier to read.

Tip #2 - Use Selectors for Selecting Specific Values from State

A Selector is a function that retrieves a specific value from the state. A Selector operates on the current state and returns a derived value. Selectors don’t modify state; they just select a specific slice of state.

For example:

const getName = (state) => state.name;

const selectName$ = state$.pipe(
  map(getName)
);

selectName$.subscribe((name) => console.log(name));

In this example, we’ve created a Selector, getName() function, that retrieves a name property from the state. We’ve then used the map operator to create a new Observable that emits only the selected value from the state. Finally, we’ve subscribed to selectName$ Observable and logged the name value.

Using Selectors can make your code more efficient, as you don’t need to process the entire state object. It also makes your code more organized, as all state values selection logic is in one single place.

Tip #3 - Use Operators for Filtering and Combining State Values

Operators are functions that transform Observables. When used with RxJS for state management, operators can be used to filter or combine state values based on specific conditions.

For example:

const evenAge$ = state$.pipe(
  map((state) => state.age),
  filter((age) => age % 2 === 0)
);

evenAge$.subscribe((age) => console.log(age));

Here, we’ve created an Observable that emits only even age values from the state. We’ve used the map operator to select the age value from the state, and then filter operator to emit only even age values.

Operators can make your code more efficient and simpler, as you don’t need to write complex if-else conditions for filtering and combining values.

Tip #4 - Use NgRx for Large-Scale State Management

If your application has complex state scenarios, it’s better to use NgRx, a state management library for Angular. NgRx is built on top of RxJS and provides a set of powerful tools for managing state in Angular.

With NgRx, you can handle complex state scenarios like caching, throttling, debouncing, and undo-redo. NgRx also provides a set of tools that help you handle side effects, such as HTTP requests and events, in a predictable manner.

Using NgRx can make your code more organized, scalable, and easier to maintain.

Tip #5 - Use Testing to Ensure the Correctness of Your State Management Code

When using RxJS for state management in Angular, it’s essential to test your code to ensure its correctness. RxJS provides a set of testing utilities that makes it easier to test Observables and Operators.

For example:

import { TestScheduler } from 'rxjs/testing';

describe('evenAge$', () => {
  let scheduler: TestScheduler;
  beforeEach(() => {
    scheduler = new TestScheduler((actual, expected) => {
      expect(actual).toEqual(expected);
    });
  });
  it('should return even age', () => {
    scheduler.run((helpers) => {
      const { expectObservable } = helpers;
      const state$ = new BehaviorSubject({
        age: 1
      });
      const evenAge$ = state$.pipe(
        map((state) => state.age),
        filter((age) => age % 2 === 0)
      );
      expectObservable(evenAge$).toBe('');
      state$.next({
        age: 2
      });
      expectObservable(evenAge$).toBe('(a|)', {
        a: 2
      });
      state$.next({
        age: 3
      });
      expectObservable(evenAge$).toBe('(a|)', {
        a: 2
      });
    });
  });
});

In this example, we’ve created a test case for evenAge$ Observable that filters even age values from the state. We’ve first created a TestScheduler instance to help us test the Observable. Then we’ve created a state$ Behavior Subject and evenAge$ Observable. Finally, we’ve tested the Observable using expectObservable.

Testing can help you identify potential issues in your code and ensure that your code is working as expected.

Conclusion

In this article, we’ve shared five tips for Angular developers using RxJS for state management. Using Behavior Subjects for initializing state, Selectors for selecting specific values from state, Operators for filtering and combining state values, NgRx for large-scale state management, and Testing to ensure the correctness of your state management code. We hope that these tips will help you improve your state management code in Angular.