fix(first): will now only emit one value in recursive cases (#2100)

adds guard after first emitted value to prevent reentrant behavior

fixes #2098

spec/operators/first-spec.ts

@@ -42,6 +42,20 @@ describe('Observable.prototype.first', () => {
  expectSubscriptions(e1.subscriptions).toBe(sub);
  });
 
+ it('should only emit one value in recursive cases', () => {
+ const subject = new Rx.Subject<number>();
+ const results = [];
+
+ subject.first().subscribe(x => {
+ results.push(x);
+ subject.next(x + 1);
+ });
+
+ subject.next(0);
+
+ expect(results).to.deep.equal([0]);
+ });
+
  it('should propagate error from the source observable', () => {
  const e1 = hot('---^---#');
  const expected = '----#';

src/operator/first.ts

@@ -85,6 +85,7 @@ class FirstOperator<T, R> implements Operator<T, R> {
 class FirstSubscriber<T, R> extends Subscriber<T> {
  private index: number = 0;
  private hasCompleted: boolean = false;
+ private _emitted: boolean = false;
 
  constructor(destination: Subscriber<R>,
  private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
@@ -137,9 +138,12 @@ class FirstSubscriber<T, R> extends Subscriber<T> {
 
  private _emitFinal(value: any) {
  const destination = this.destination;
- destination.next(value);
- destination.complete();
- this.hasCompleted = true;
+ if (!this._emitted) {
+ this._emitted = true;
+ destination.next(value);
+ destination.complete();
+ this.hasCompleted = true;
+ }
  }
 
  protected _complete(): void {