rxjs-examples

ignoreFalsyValues.ts

import { someDataSource } from './some-api.service';
import { ignoreFalsySignals, tapLog } from 'rxjs-toolkit';

interface Signal {
  foo: string;
}

/** 
 * signals$ pushes out an Observable of Signal
 * imagine the source of the stream is the return from an API call
 * when the stream first connects via the subscription
 * the signal value could be undefined
 */ 
someDataSource.signals$.pipe(
  /**
   * this does not cut the stream off
   * instead, it will only let truthy values through
   * once a JSON payload from an API request arrives
   * the data will flow through into the next callback of the Subscription
   */
  tapLog(), // undefined, { foo: 'hello rxjs world' }
  ignoreFalsySignals(),
  tapLog(), // { foo: 'hello rxjs world' }
).subscribe({
  next(signal) {
    doFooThings(signal.foo); // we've guaranteed that the signal is not undefined
  }
});