text: import { EmptyError } from '../util/EmptyError';
  import { filter } from './filter';
  import { take } from './take';
  import { defaultIfEmpty } from './defaultIfEmpty';
  import { throwIfEmpty } from './throwIfEmpty';
  import { identity } from '../util/identity';
  /**
   * Emits only the first value (or the first value that meets some condition)
   * emitted by the source Observable.
   *
   * <span class="informal">Emits only the first value. Or emits only the first
   * value that passes some test.</span>
   *
   * <img src="./img/first.png" width="100%">
   *
   * If called with no arguments, `first` emits the first value of the source
   * Observable, then completes. If called with a `predicate` function, `first`
   * emits the first value of the source that matches the specified condition. It
   * may also take a `resultSelector` function to produce the output value from
   * the input value, and a `defaultValue` to emit in case the source completes
   * before it is able to emit a valid value. Throws an error if `defaultValue`
   * was not provided and a matching element is not found.
   *
   * @example <caption>Emit only the first click that happens on the DOM</caption>
   * var clicks = Rx.Observable.fromEvent(document, 'click');
   * var result = clicks.first();
   * result.subscribe(x => console.log(x));
   *
   * @example <caption>Emits the first click that happens on a DIV</caption>
   * var clicks = Rx.Observable.fromEvent(document, 'click');
   * var result = clicks.first(ev => ev.target.tagName === 'DIV');
   * result.subscribe(x => console.log(x));
   *
   * @see {@link filter}
   * @see {@link find}
   * @see {@link take}
   *
   * @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
   * callback if the Observable completes before any `next` notification was sent.
   *
   * @param {function(value: T, index: number, source: Observable<T>): boolean} [predicate]
   * An optional function called with each item to test for condition matching.
   * @param {R} [defaultValue] The default value emitted in case no valid value
   * was found on the source.
   * @return {Observable<T|R>} An Observable of the first item that matches the
   * condition.
   * @method first
   * @owner Observable
   */
  export function first(predicate, defaultValue) {
      const hasDefaultValue = arguments.length >= 2;
      return (source) => source.pipe(predicate ? filter((v, i) => predicate(v, i, source)) : identity, take(1), hasDefaultValue ? defaultIfEmpty(defaultValue) : throwIfEmpty(() => new EmptyError()));
  }
  //# sourceMappingURL=first.js.map