Attempt to fix lazy loader spec transient failure

app/assets/javascripts/lazy_loader.js

@@ -19,7 +19,7 @@ export default class LazyLoader {
   }
 
   searchLazyImages() {
-    requestIdleCallback(
+    window.requestIdleCallback(
       () => {
         const lazyImages = [].slice.call(document.querySelectorAll('.lazy'));
 
@@ -107,7 +107,7 @@ export default class LazyLoader {
   }
 
   scrollCheck() {
-    requestAnimationFrame(() => this.checkElementsInView());
+    window.requestAnimationFrame(() => this.checkElementsInView());
   }
 
   checkElementsInView() {
@@ -122,7 +122,7 @@ export default class LazyLoader {
         const imgBound = imgTop + imgBoundRect.height;
 
         if (scrollTop <= imgBound && visHeight >= imgTop) {
-          requestAnimationFrame(() => {
+          window.requestAnimationFrame(() => {
             LazyLoader.loadImage(selectedImage);
           });
           return false;

spec/javascripts/helpers/scroll_into_view_promise.js

+export default function scrollIntoViewPromise(intersectionTarget, timeout = 100, maxTries = 5) {
+  return new Promise((resolve, reject) => {
+    let intersectionObserver;
+    let retry = 0;
+
+    const intervalId = setInterval(() => {
+      if (retry >= maxTries) {
+        intersectionObserver.disconnect();
+        clearInterval(intervalId);
+        reject(new Error(`Could not scroll target into viewPort within ${timeout * maxTries} ms`));
+      }
+      retry += 1;
+      intersectionTarget.scrollIntoView();
+    }, timeout);
+
+    intersectionObserver = new IntersectionObserver(entries => {
+      if (entries[0].isIntersecting) {
+        intersectionObserver.disconnect();
+        clearInterval(intervalId);
+        resolve();
+      }
+    });
+
+    intersectionObserver.observe(intersectionTarget);
+
+    intersectionTarget.scrollIntoView();
+  });
+}

spec/javascripts/helpers/wait_for_attribute_change.js

+export default (domElement, attributes, timeout = 1500) =>
+  new Promise((resolve, reject) => {
+    let observer;
+    const timeoutId = setTimeout(() => {
+      observer.disconnect();
+      reject(new Error(`Could not see an attribute update within ${timeout} ms`));
+    }, timeout);
+
+    observer = new MutationObserver(() => {
+      clearTimeout(timeoutId);
+      observer.disconnect();
+      resolve();
+    });
+
+    observer.observe(domElement, { attributes: true, attributeFilter: attributes });
+  });

spec/javascripts/lazy_loader_spec.js

 import LazyLoader from '~/lazy_loader';
 import { TEST_HOST } from './test_constants';
-
-let lazyLoader = null;
+import scrollIntoViewPromise from './helpers/scroll_into_view_promise';
+import waitForPromises from './helpers/wait_for_promises';
+import waitForAttributeChange from './helpers/wait_for_attribute_change';
 
 const execImmediately = callback => {
   callback();
 };
 
 describe('LazyLoader', function() {
+  let lazyLoader = null;
+
   preloadFixtures('issues/issue_with_comment.html.raw');
 
-  describe('with IntersectionObserver disabled', () => {
+  describe('without IntersectionObserver', () => {
     beforeEach(function() {
       loadFixtures('issues/issue_with_comment.html.raw');
 
@@ -36,14 +39,15 @@ describe('LazyLoader', function() {
     it('should copy value from data-src to src for img 1', function(done) {
       const img = document.querySelectorAll('img[data-src]')[0];
       const originalDataSrc = img.getAttribute('data-src');
-      img.scrollIntoView();
 
-      setTimeout(() => {
+      Promise.all([scrollIntoViewPromise(img), waitForAttributeChange(img, ['data-src', 'src'])])
+        .then(() => {
           expect(LazyLoader.loadImage).toHaveBeenCalled();
           expect(img.getAttribute('src')).toBe(originalDataSrc);
           expect(img).toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should lazy load dynamically added data-src images', function(done) {
@@ -52,14 +56,18 @@ describe('LazyLoader', function() {
       newImg.className = 'lazy';
       newImg.setAttribute('data-src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      Promise.all([
+        scrollIntoViewPromise(newImg),
+        waitForAttributeChange(newImg, ['data-src', 'src']),
+      ])
+        .then(() => {
           expect(LazyLoader.loadImage).toHaveBeenCalled();
           expect(newImg.getAttribute('src')).toBe(testPath);
           expect(newImg).toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should not alter normal images', function(done) {
@@ -67,13 +75,15 @@ describe('LazyLoader', function() {
       const testPath = `${TEST_HOST}/img/testimg.png`;
       newImg.setAttribute('src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      scrollIntoViewPromise(newImg)
+        .then(waitForPromises)
+        .then(() => {
           expect(LazyLoader.loadImage).not.toHaveBeenCalled();
           expect(newImg).not.toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should not load dynamically added pictures if content observer is turned off', done => {
@@ -84,13 +94,15 @@ describe('LazyLoader', function() {
       newImg.className = 'lazy';
       newImg.setAttribute('data-src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      scrollIntoViewPromise(newImg)
+        .then(waitForPromises)
+        .then(() => {
           expect(LazyLoader.loadImage).not.toHaveBeenCalled();
           expect(newImg).not.toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should load dynamically added pictures if content observer is turned off and on again', done => {
@@ -102,17 +114,22 @@ describe('LazyLoader', function() {
       newImg.className = 'lazy';
       newImg.setAttribute('data-src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      Promise.all([
+        scrollIntoViewPromise(newImg),
+        waitForAttributeChange(newImg, ['data-src', 'src']),
+      ])
+        .then(waitForPromises)
+        .then(() => {
           expect(LazyLoader.loadImage).toHaveBeenCalled();
           expect(newImg).toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
   });
 
-  describe('with IntersectionObserver enabled', () => {
+  describe('with IntersectionObserver', () => {
     beforeEach(function() {
       loadFixtures('issues/issue_with_comment.html.raw');
 
@@ -136,14 +153,15 @@ describe('LazyLoader', function() {
     it('should copy value from data-src to src for img 1', function(done) {
       const img = document.querySelectorAll('img[data-src]')[0];
       const originalDataSrc = img.getAttribute('data-src');
-      img.scrollIntoView();
 
-      setTimeout(() => {
+      Promise.all([scrollIntoViewPromise(img), waitForAttributeChange(img, ['data-src', 'src'])])
+        .then(() => {
           expect(LazyLoader.loadImage).toHaveBeenCalled();
           expect(img.getAttribute('src')).toBe(originalDataSrc);
           expect(img).toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should lazy load dynamically added data-src images', function(done) {
@@ -152,14 +170,18 @@ describe('LazyLoader', function() {
       newImg.className = 'lazy';
       newImg.setAttribute('data-src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      Promise.all([
+        scrollIntoViewPromise(newImg),
+        waitForAttributeChange(newImg, ['data-src', 'src']),
+      ])
+        .then(() => {
           expect(LazyLoader.loadImage).toHaveBeenCalled();
           expect(newImg.getAttribute('src')).toBe(testPath);
           expect(newImg).toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should not alter normal images', function(done) {
@@ -167,13 +189,15 @@ describe('LazyLoader', function() {
       const testPath = `${TEST_HOST}/img/testimg.png`;
       newImg.setAttribute('src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      scrollIntoViewPromise(newImg)
+        .then(waitForPromises)
+        .then(() => {
           expect(LazyLoader.loadImage).not.toHaveBeenCalled();
           expect(newImg).not.toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should not load dynamically added pictures if content observer is turned off', done => {
@@ -184,13 +208,15 @@ describe('LazyLoader', function() {
       newImg.className = 'lazy';
       newImg.setAttribute('data-src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      scrollIntoViewPromise(newImg)
+        .then(waitForPromises)
+        .then(() => {
           expect(LazyLoader.loadImage).not.toHaveBeenCalled();
           expect(newImg).not.toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
 
     it('should load dynamically added pictures if content observer is turned off and on again', done => {
@@ -202,13 +228,17 @@ describe('LazyLoader', function() {
       newImg.className = 'lazy';
       newImg.setAttribute('data-src', testPath);
       document.body.appendChild(newImg);
-      newImg.scrollIntoView();
 
-      setTimeout(() => {
+      Promise.all([
+        scrollIntoViewPromise(newImg),
+        waitForAttributeChange(newImg, ['data-src', 'src']),
+      ])
+        .then(() => {
           expect(LazyLoader.loadImage).toHaveBeenCalled();
           expect(newImg).toHaveClass('js-lazy-loaded');
           done();
-      }, 50);
+        })
+        .catch(done.fail);
     });
   });
 });