Do not trigger slideChange on the initial render.

extensions/amp-base-carousel/0.1/carousel.js

@@ -680,13 +680,18 @@ export class Carousel {
   }
 
   /**
-   * Updates the resting index as well as firing an event.
+   * Updates the resting index as well as firing an event, if it actually
+   * changed.
    * @param {number} restingIndex The new resting index.
    * @param {ActionSource=} actionSource The actionSource associated with this
    *    change.
    * @private
    */
   updateRestingIndex_(restingIndex, actionSource) {
+    if (this.restingIndex_ == restingIndex) {
+      return;
+    }
+
     this.restingIndex_ = restingIndex;
     this.element_.dispatchEvent(
       createCustomEvent(

extensions/amp-carousel/0.2/amp-carousel.js

@@ -510,13 +510,27 @@ class AmpCarousel extends AMP.BaseElement {
   }
 
   /**
-   * Updates the current index, resuming the current slide and pausing all
-   * others.
+   * Updates the current index, triggering actions and analytics events.
    * @param {number} index
+   * @param {!ActionSource} actionSource
    */
-  updateCurrentIndex_(index) {
+  updateCurrentIndex_(index, actionSource) {
     const prevIndex = this.currentIndex_;
     this.currentIndex_ = index;
+
+    // Ignore the first indexChange, we do not want to trigger any events.
+    if (prevIndex == null) {
+      return;
+    }
+
+    const data = dict({'index': index});
+    const name = 'slideChange';
+    const isHighTrust = this.isHighTrustActionSource_(actionSource);
+    const trust = isHighTrust ? ActionTrust.HIGH : ActionTrust.LOW;
+
+    const action = createCustomEvent(this.win, `slidescroll.${name}`, data);
+    this.action_.trigger(this.element, name, action, trust);
+    this.element.dispatchCustomEvent(name, data);
     this.triggerAnalyticsEvent_(prevIndex, index);
   }
 
@@ -618,16 +632,9 @@ class AmpCarousel extends AMP.BaseElement {
     const detail = getDetail(event);
     const index = detail['index'];
     const actionSource = detail['actionSource'];
-    const data = dict({'index': index});
-    const name = 'slideChange';
-    const isHighTrust = this.isHighTrustActionSource_(actionSource);
-    const trust = isHighTrust ? ActionTrust.HIGH : ActionTrust.LOW;
 
-    const action = createCustomEvent(this.win, `slidescroll.${name}`, data);
-    this.action_.trigger(this.element, name, action, trust);
-    this.element.dispatchCustomEvent(name, data);
     this.hadTouch_ = this.hadTouch_ || actionSource == ActionSource.TOUCH;
-    this.updateCurrentIndex_(index);
+    this.updateCurrentIndex_(index, actionSource);
     this.updateUi_();
   }
 }

extensions/amp-carousel/0.2/test/test-type-slides.js

@@ -201,6 +201,27 @@ describes.realWin(
       });
     });
 
+    describe('slideChange event', () => {
+      it('should not dispatch on initial render', async () => {
+        const eventSpy = sandbox.spy();
+        container.addEventListener('slideChange', eventSpy);
+        await getCarousel({loop: false});
+
+        expect(eventSpy).to.have.not.been.called;
+      });
+
+      it('should dispatch when changing slides', async () => {
+        const eventSpy = sandbox.spy();
+        container.addEventListener('slideChange', eventSpy);
+        const carousel = await getCarousel({loop: false});
+
+        carousel.implementation_.interactionNext();
+        await afterIndexUpdate(carousel);
+
+        expect(eventSpy).to.have.been.calledOnce;
+      });
+    });
+
     describe('goToSlide action', () => {
       it('should propagate high trust', async () => {
         const carousel = await getCarousel({loop: false});