initial commit: scaffolding

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diff --git a/node_modules/rxjs/src/internal/operators/last.ts b/node_modules/rxjs/src/internal/operators/last.ts
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+import { Observable } from '../Observable';
+import { EmptyError } from '../util/EmptyError';
+import { OperatorFunction, TruthyTypesOf } from '../types';
+import { filter } from './filter';
+import { takeLast } from './takeLast';
+import { throwIfEmpty } from './throwIfEmpty';
+import { defaultIfEmpty } from './defaultIfEmpty';
+import { identity } from '../util/identity';
+
+export function last<T>(predicate: BooleanConstructor): OperatorFunction<T, TruthyTypesOf<T>>;
+export function last<T, D>(predicate: BooleanConstructor, defaultValue: D): OperatorFunction<T, TruthyTypesOf<T> | D>;
+export function last<T, D = T>(predicate?: null, defaultValue?: D): OperatorFunction<T, T | D>;
+export function last<T, S extends T>(
+  predicate: (value: T, index: number, source: Observable<T>) => value is S,
+  defaultValue?: S
+): OperatorFunction<T, S>;
+export function last<T, D = T>(
+  predicate: (value: T, index: number, source: Observable<T>) => boolean,
+  defaultValue?: D
+): OperatorFunction<T, T | D>;
+
+/**
+ * Returns an Observable that emits only the last item emitted by the source Observable.
+ * It optionally takes a predicate function as a parameter, in which case, rather than emitting
+ * the last item from the source Observable, the resulting Observable will emit the last item
+ * from the source Observable that satisfies the predicate.
+ *
+ * ![](last.png)
+ *
+ * It will emit an error notification if the source completes without notification or one that matches
+ * the predicate. It returns the last value or if a predicate is provided last value that matches the
+ * predicate. It returns the given default value if no notification is emitted or matches the predicate.
+ *
+ * ## Examples
+ *
+ * Last alphabet from the sequence
+ *
+ * ```ts
+ * import { from, last } from 'rxjs';
+ *
+ * const source = from(['x', 'y', 'z']);
+ * const result = source.pipe(last());
+ *
+ * result.subscribe(value => console.log(`Last alphabet: ${ value }`));
+ *
+ * // Outputs
+ * // Last alphabet: z
+ * ```
+ *
+ * Default value when the value in the predicate is not matched
+ *
+ * ```ts
+ * import { from, last } from 'rxjs';
+ *
+ * const source = from(['x', 'y', 'z']);
+ * const result = source.pipe(last(char => char === 'a', 'not found'));
+ *
+ * result.subscribe(value => console.log(`'a' is ${ value }.`));
+ *
+ * // Outputs
+ * // 'a' is not found.
+ * ```
+ *
+ * @see {@link skip}
+ * @see {@link skipUntil}
+ * @see {@link skipLast}
+ * @see {@link skipWhile}
+ * @see {@link first}
+ *
+ * @throws {EmptyError} Delivers an `EmptyError` to the Observer's `error`
+ * callback if the Observable completes before any `next` notification was sent.
+ *
+ * @param predicate The condition any source emitted item has to satisfy.
+ * @param defaultValue An optional default value to provide if last `predicate`
+ * isn't met or no values were emitted.
+ * @return A function that returns an Observable that emits only the last item
+ * satisfying the given condition from the source, or an error notification
+ * with an `EmptyError` object if no such items are emitted.
+ */
+export function last<T, D>(
+  predicate?: ((value: T, index: number, source: Observable<T>) => boolean) | null,
+  defaultValue?: D
+): OperatorFunction<T, T | D> {
+  const hasDefaultValue = arguments.length >= 2;
+  return (source: Observable<T>) =>
+    source.pipe(
+      predicate ? filter((v, i) => predicate(v, i, source)) : identity,
+      takeLast(1),
+      hasDefaultValue ? defaultIfEmpty(defaultValue!) : throwIfEmpty(() => new EmptyError())
+    );
+}