# @code-art/rx-helpers

## About the library

A library with [Rxjs](https://rxjs-dev.firebaseapp.com/) operators that can be used in your [Angular 9](https://angular.io) projects.

## Consuming the library

### 1. Installing the library

To install the library in your Angular application you need to run the following commands:

```bash
$ npm install @code-art/rx-helpers --save
```
or

```bash
$ yarn add @code-art/rx-helpers
```

### 2. Using withZone operator

The withZone operator will cause the observable next, error and complete callbacks to be executed withing an Angular `NgZone`. This is useful when having asynchronous events that are triggered outside Angular such as a server event using websockets, etc.

```typescript
import { Component, OnInit, NgZone } from '@angular/core';
import { Observable, Subject } from 'rxjs';
import { withZone } from '@code-art/rx-helpers';

@Component({
  selector: 'app-with-zone-example',
  templateUrl: './with-zone-example.component.html',
})
export class WithZoneExampleComponent  {

  timerSubject = new Subject<number>();
  timerWithZone: Observable<number>;
  private _value = 1;
  constructor(private readonly zone: NgZone) {
    this.timerWithZone = this.timerSubject.pipe(withZone(this.zone));
    zone.runOutsideAngular(() => {
      // The next operator executes outside angular.
      setInterval(() => this.timerSubject.next(this._value++), 1000);
    });
   }
}

```

### 3. Using takeUntilDestroyed operator

The `takeUntilDestroyed` operator will cause the observable to emit values until a component, pipe or directive are destroyed (ngOnDestroy called). 

**Note**: Starting with Angular 9 the `@TakeUntilDestroyed` decorator needs to be applied to components, directives, pipes and services with Ivy.

```typescript
import { Component, OnInit, OnDestroy } from '@angular/core';
import { timer } from 'rxjs';
import { takeUntilDestroyed, TakeUntilDestroyed } from '@code-art/rx-helpers';

/* The following decorator is needed for components, directives, pipes and services when using Ivy */
@TakeUntilDestroyed() 
@Component({
  selector: 'app-take-until-destroyed-example',
  templateUrl: './take-until-destroyed-example.component.html',
})
export class TakeUntilDestroyedExampleComponent implements OnDestroy {
  timer = timer(1000, 1000).pipe(takeUntilDestroyed(this));

  constructor() {
    this.timer.subscribe(() => {}, () => {}, () => {
      console.log('completed');
    });
  }

  ngOnDestroy(): void {
    console.log('destroyed');
  }
}
```

### 4. using cacheUntil operator

The `cacheUntil` operator will subscribe to the observable and cache first emission until provided observable emits, then it will resubscribe. 


```typescript

const currentTime = new Observable<Date>(observer => {
  observer.next(new Date());
  observer.complete();
  return {
    unsubscribe: () => {},
  };
});

const s = new Subject();
const obs = currentTime.pipe(
  cacheUntil(s);
);

let d: Date | null = null; // d === null
let complete = false;
const sub = obs.subscribe({
    next: (v) => d = v,
    complete: () => complete = true;
  }
);

// d has a non null value now
// complete is false.

s.next(0); // d has a new value
s.complete(); // complete === true

sub.unsubscribe();
```
## License

MIT © Sherif Elmetainy \(Code Art\)