🐛Remove text nodes from amp-story on build (ampproject#22918)

* Remove text nodes from amp-story and add tests

* Make prettier happy

* Clean up debug statements.

* Use childNodes helper to find text nodes instead of Array.from

Author: maribethb

extensions/amp-story/1.0/amp-story.js

@@ -86,6 +86,7 @@ import {
   childElement,
   childElementByTag,
   childElements,
+  childNodes,
   closest,
   createElementWithAttributes,
   isRTL,
@@ -442,6 +443,15 @@ export class AmpStory extends AMP.BaseElement {
     // hover. (See 17654)
     this.element.removeAttribute('title');
 
+    // Remove text nodes which would be shown outside of the amp-story
+    const textNodes = childNodes(
+      this.element,
+      node => node.nodeType === Node.TEXT_NODE
+    );
+    textNodes.forEach(node => {
+      this.element.removeChild(node);
+    });
+
     if (isExperimentOn(this.win, 'amp-story-branching')) {
       this.registerAction('goToPage', invocation => {
         const {args} = invocation;

extensions/amp-story/1.0/test/test-amp-story.js

@@ -183,6 +183,17 @@ describes.realWin(
       });
     });
 
+    it('should remove text child nodes when built', () => {
+      createPages(story.element, 1, ['cover']);
+      const textToRemove = 'this should be removed';
+      const textNode = win.document.createTextNode(textToRemove);
+      story.element.appendChild(textNode);
+      story.buildCallback();
+      return story.layoutCallback().then(() => {
+        expect(story.element.innerText).to.not.have.string(textToRemove);
+      });
+    });
+
     it('should preload the bookend if navigating to the last page', () => {
       createPages(story.element, 1, ['cover']);