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node_modules/rxjs/_esm2015/operators/first.js

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+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.
+ *
+ * <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 {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<T|R>} 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