feat(publishLast): add publishLast operator

closes ReactiveX#883

spec/operators/publishLast-spec.js

@@ -0,0 +1,222 @@
+/* globals describe, it, expect, expectObservable, expectSubscriptions, hot, cold */
+var Rx = require('../../dist/cjs/Rx');
+var Observable = Rx.Observable;
+var Subject = Rx.Subject;
+
+describe('Observable.prototype.publishLast()', function () {
+  it('should return a ConnectableObservable', function () {
+    var source = Observable.of(1).publishLast();
+
+    expect(source instanceof Rx.ConnectableObservable).toBe(true);
+  });
+
+  it('should emit last notification of a simple source Observable', function () {
+    var source = cold('--1-2---3-4--5-|');
+    var sourceSubs =  '^              !';
+    var published = source.publishLast();
+    var expected =    '---------------(5|)';
+
+    expectObservable(published).toBe(expected);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    published.connect();
+  });
+
+  it('should do nothing if connect is not called, despite subscriptions', function () {
+    var source = cold('--1-2---3-4--5-|');
+    var sourceSubs = [];
+    var published = source.publishLast();
+    var expected =    '-';
+
+    expectObservable(published).toBe(expected);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+  });
+
+  it('should multicast the same values to multiple observers', function () {
+    var source =     cold('-1-2-3----4-|');
+    var sourceSubs =      '^           !';
+    var published = source.publishLast();
+    var subscriber1 = hot('a|           ').mergeMapTo(published);
+    var expected1   =     '------------(4|)';
+    var subscriber2 = hot('    b|       ').mergeMapTo(published);
+    var expected2   =     '    --------(4|)';
+    var subscriber3 = hot('        c|   ').mergeMapTo(published);
+    var expected3   =     '        ----(4|)';
+
+    expectObservable(subscriber1).toBe(expected1);
+    expectObservable(subscriber2).toBe(expected2);
+    expectObservable(subscriber3).toBe(expected3);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    published.connect();
+  });
+
+  it('should multicast an error from the source to multiple observers', function () {
+    var source =     cold('-1-2-3----4-#');
+    var sourceSubs =      '^           !';
+    var published = source.publishLast();
+    var subscriber1 = hot('a|           ').mergeMapTo(published);
+    var expected1   =     '------------#';
+    var subscriber2 = hot('    b|       ').mergeMapTo(published);
+    var expected2   =     '    --------#';
+    var subscriber3 = hot('        c|   ').mergeMapTo(published);
+    var expected3   =     '        ----#';
+
+    expectObservable(subscriber1).toBe(expected1);
+    expectObservable(subscriber2).toBe(expected2);
+    expectObservable(subscriber3).toBe(expected3);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    published.connect();
+  });
+
+  it('should not cast any values to multiple observers, ' +
+  'when source is unsubscribed explicitly and early', function () {
+    var source =     cold('-1-2-3----4-|');
+    var sourceSubs =      '^        !   ';
+    var published = source.publishLast();
+    var unsub =           '         u   ';
+    var subscriber1 = hot('a|           ').mergeMapTo(published);
+    var expected1   =     '----------   ';
+    var subscriber2 = hot('    b|       ').mergeMapTo(published);
+    var expected2   =     '    ------   ';
+    var subscriber3 = hot('        c|   ').mergeMapTo(published);
+    var expected3   =     '        --   ';
+
+    expectObservable(subscriber1).toBe(expected1);
+    expectObservable(subscriber2).toBe(expected2);
+    expectObservable(subscriber3).toBe(expected3);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    // Set up unsubscription action
+    var connection;
+    expectObservable(hot(unsub).do(function () {
+      connection.unsubscribe();
+    })).toBe(unsub);
+
+    connection = published.connect();
+  });
+
+  describe('with refCount()', function () {
+    it('should connect when first subscriber subscribes', function () {
+      var source =     cold(   '-1-2-3----4-|');
+      var sourceSubs =      '   ^           !';
+      var replayed = source.publishLast().refCount();
+      var subscriber1 = hot('   a|           ').mergeMapTo(replayed);
+      var expected1   =     '   ------------(4|)';
+      var subscriber2 = hot('       b|       ').mergeMapTo(replayed);
+      var expected2   =     '       --------(4|)';
+      var subscriber3 = hot('           c|   ').mergeMapTo(replayed);
+      var expected3   =     '           ----(4|)';
+
+      expectObservable(subscriber1).toBe(expected1);
+      expectObservable(subscriber2).toBe(expected2);
+      expectObservable(subscriber3).toBe(expected3);
+      expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+    });
+
+    it('should disconnect when last subscriber unsubscribes', function () {
+      var source =     cold(   '-1-2-3----4-|');
+      var sourceSubs =      '   ^        !   ';
+      var replayed = source.publishLast().refCount();
+      var subscriber1 = hot('   a|           ').mergeMapTo(replayed);
+      var unsub1 =          '          !     ';
+      var expected1   =     '   --------     ';
+      var subscriber2 = hot('       b|       ').mergeMapTo(replayed);
+      var unsub2 =          '            !   ';
+      var expected2   =     '       ------   ';
+
+      expectObservable(subscriber1, unsub1).toBe(expected1);
+      expectObservable(subscriber2, unsub2).toBe(expected2);
+      expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+    });
+
+    it('should NOT be retryable', function () {
+      var source =     cold('-1-2-3----4-#');
+      var sourceSubs =      '^           !';
+      var published = source.publishLast().refCount().retry(3);
+      var subscriber1 = hot('a|           ').mergeMapTo(published);
+      var expected1   =     '------------#';
+      var subscriber2 = hot('    b|       ').mergeMapTo(published);
+      var expected2   =     '    --------#';
+      var subscriber3 = hot('        c|   ').mergeMapTo(published);
+      var expected3   =     '        ----#';
+
+      expectObservable(subscriber1).toBe(expected1);
+      expectObservable(subscriber2).toBe(expected2);
+      expectObservable(subscriber3).toBe(expected3);
+      expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+    });
+  });
+
+  it('should multicast an empty source', function () {
+    var source = cold('|');
+    var sourceSubs =  '(^!)';
+    var published = source.publishLast();
+    var expected =    '|';
+
+    expectObservable(published).toBe(expected);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    published.connect();
+  });
+
+  it('should multicast a never source', function () {
+    var source = cold('-');
+    var sourceSubs =  '^';
+    var published = source.publishLast();
+    var expected =    '-';
+
+    expectObservable(published).toBe(expected);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    published.connect();
+  });
+
+  it('should multicast a throw source', function () {
+    var source = cold('#');
+    var sourceSubs =  '(^!)';
+    var published = source.publishLast();
+    var expected =    '#';
+
+    expectObservable(published).toBe(expected);
+    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
+
+    published.connect();
+  });
+
+  it('should multicast one observable to multiple observers', function (done) {
+    var results1 = [];
+    var results2 = [];
+    var subscriptions = 0;
+
+    var source = new Observable(function (observer) {
+      subscriptions++;
+      observer.next(1);
+      observer.next(2);
+      observer.next(3);
+      observer.next(4);
+      observer.complete();
+    });
+
+    var connectable = source.publishLast();
+
+    connectable.subscribe(function (x) {
+      results1.push(x);
+    });
+
+    connectable.subscribe(function (x) {
+      results2.push(x);
+    });
+
+    expect(results1).toEqual([]);
+    expect(results2).toEqual([]);
+
+    connectable.connect();
+
+    expect(results1).toEqual([4]);
+    expect(results2).toEqual([4]);
+    expect(subscriptions).toBe(1);
+    done();
+  });
+});

src/CoreOperators.ts

@@ -57,6 +57,7 @@ export interface CoreOperators<T> {
   publish?: () => ConnectableObservable<T>;
   publishBehavior?: (value: any) => ConnectableObservable<T>;
   publishReplay?: (bufferSize?: number, windowTime?: number, scheduler?: Scheduler) => ConnectableObservable<T>;
+  publishLast?: () => ConnectableObservable<T>;
   reduce?: <R>(project: (acc: R, x: T) => R, seed?: R) => Observable<R>;
   repeat?: (count?: number) => Observable<T>;
   retry?: (count?: number) => Observable<T>;

src/Observable.ts

@@ -217,6 +217,7 @@ export class Observable<T> implements CoreOperators<T>  {
   publish: () => ConnectableObservable<T>;
   publishBehavior: (value: any) => ConnectableObservable<T>;
   publishReplay: (bufferSize?: number, windowTime?: number, scheduler?: Scheduler) => ConnectableObservable<T>;
+  publishLast: () => ConnectableObservable<T>;
   reduce: <R>(project: (acc: R, x: T) => R, seed?: R) => Observable<R>;
   repeat: (count?: number) => Observable<T>;
   retry: (count?: number) => Observable<T>;

src/Rx.KitchenSink.ts

@@ -91,6 +91,7 @@ import './operator/partition';
 import './operator/publish';
 import './operator/publishBehavior';
 import './operator/publishReplay';
+import './operator/publishLast';
 import './operator/reduce';
 import './operator/repeat';
 import './operator/retry';

src/Rx.ts

@@ -69,6 +69,7 @@ import './operator/partition';
 import './operator/publish';
 import './operator/publishBehavior';
 import './operator/publishReplay';
+import './operator/publishLast';
 import './operator/reduce';
 import './operator/repeat';
 import './operator/retry';

src/operator/publishLast.ts

@@ -0,0 +1,10 @@
+import {AsyncSubject} from '../subject/AsyncSubject';
+import {Observable} from '../Observable';
+import {multicast} from './multicast';
+import {ConnectableObservable} from '../observable/ConnectableObservable';
+
+export function publishLast<T>(): ConnectableObservable<T> {
+  return multicast.call(this, new AsyncSubject());
+}
+
+Observable.prototype.publishLast = publishLast;