import { Subscriber } from '../Subscriber'; import { EmptyError } from '../util/EmptyError'; /** * Emits only the first value (or the first value that meets some condition) * emitted by the source Observable. * * Emits only the first value. Or emits only the first * value that passes some test. * * * * 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 Emit only the first click that happens on the DOM * var clicks = Rx.Observable.fromEvent(document, 'click'); * var result = clicks.first(); * result.subscribe(x => console.log(x)); * * @example Emits the first click that happens on a DIV * 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): boolean} [predicate] * An optional function called with each item to test for condition matching. * @param {function(value: T, index: number): R} [resultSelector] A function to * produce the value on the output Observable based on the values * and the indices of the source Observable. The arguments passed to this * function are: * - `value`: the value that was emitted on the source. * - `index`: the "index" of the value from the source. * @param {R} [defaultValue] The default value emitted in case no valid value * was found on the source. * @return {Observable} An Observable of the first item that matches the * condition. * @method first * @owner Observable */ export function first(predicate, resultSelector, defaultValue) { return (source) => source.lift(new FirstOperator(predicate, resultSelector, defaultValue, source)); } class FirstOperator { constructor(predicate, resultSelector, defaultValue, source) { this.predicate = predicate; this.resultSelector = resultSelector; this.defaultValue = defaultValue; this.source = source; } call(observer, source) { return source.subscribe(new FirstSubscriber(observer, this.predicate, this.resultSelector, this.defaultValue, this.source)); } } /** * We need this JSDoc comment for affecting ESDoc. * @ignore * @extends {Ignored} */ class FirstSubscriber extends Subscriber { constructor(destination, predicate, resultSelector, defaultValue, source) { super(destination); this.predicate = predicate; this.resultSelector = resultSelector; this.defaultValue = defaultValue; this.source = source; this.index = 0; this.hasCompleted = false; this._emitted = false; } _next(value) { const index = this.index++; if (this.predicate) { this._tryPredicate(value, index); } else { this._emit(value, index); } } _tryPredicate(value, index) { let result; try { result = this.predicate(value, index, this.source); } catch (err) { this.destination.error(err); return; } if (result) { this._emit(value, index); } } _emit(value, index) { if (this.resultSelector) { this._tryResultSelector(value, index); return; } this._emitFinal(value); } _tryResultSelector(value, index) { let result; try { result = this.resultSelector(value, index); } catch (err) { this.destination.error(err); return; } this._emitFinal(result); } _emitFinal(value) { const destination = this.destination; if (!this._emitted) { this._emitted = true; destination.next(value); destination.complete(); this.hasCompleted = true; } } _complete() { const destination = this.destination; if (!this.hasCompleted && typeof this.defaultValue !== 'undefined') { destination.next(this.defaultValue); destination.complete(); } else if (!this.hasCompleted) { destination.error(new EmptyError); } } } //# sourceMappingURL=first.js.map