gitlab-org--gitlab-foss/spec/javascripts/lazy_loader_spec.js

import LazyLoader from '~/lazy_loader';
import { TEST_HOST } from './test_constants';
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');

  describe('without IntersectionObserver', () => {
    beforeEach(function() {
      loadFixtures('issues/issue_with_comment.html');

      lazyLoader = new LazyLoader({
        observerNode: 'foobar',
      });

      spyOn(LazyLoader, 'supportsIntersectionObserver').and.callFake(() => false);

      spyOn(LazyLoader, 'loadImage').and.callThrough();

      spyOn(window, 'requestAnimationFrame').and.callFake(execImmediately);
      spyOn(window, 'requestIdleCallback').and.callFake(execImmediately);

      // Doing everything that happens normally in onload
      lazyLoader.register();
    });

    afterEach(() => {
      lazyLoader.unregister();
    });

    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');

      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();
        })
        .catch(done.fail);
    });

    it('should lazy load dynamically added data-src images', function(done) {
      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.className = 'lazy';
      newImg.setAttribute('data-src', testPath);
      document.body.appendChild(newImg);

      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();
        })
        .catch(done.fail);
    });

    it('should not alter normal images', function(done) {
      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.setAttribute('src', testPath);
      document.body.appendChild(newImg);

      scrollIntoViewPromise(newImg)
        .then(waitForPromises)
        .then(() => {
          expect(LazyLoader.loadImage).not.toHaveBeenCalled();
          expect(newImg).not.toHaveClass('js-lazy-loaded');
          done();
        })
        .catch(done.fail);
    });

    it('should not load dynamically added pictures if content observer is turned off', done => {
      lazyLoader.stopContentObserver();

      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.className = 'lazy';
      newImg.setAttribute('data-src', testPath);
      document.body.appendChild(newImg);

      scrollIntoViewPromise(newImg)
        .then(waitForPromises)
        .then(() => {
          expect(LazyLoader.loadImage).not.toHaveBeenCalled();
          expect(newImg).not.toHaveClass('js-lazy-loaded');
          done();
        })
        .catch(done.fail);
    });

    it('should load dynamically added pictures if content observer is turned off and on again', done => {
      lazyLoader.stopContentObserver();
      lazyLoader.startContentObserver();

      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.className = 'lazy';
      newImg.setAttribute('data-src', testPath);
      document.body.appendChild(newImg);

      Promise.all([
        scrollIntoViewPromise(newImg),
        waitForAttributeChange(newImg, ['data-src', 'src']),
      ])
        .then(waitForPromises)
        .then(() => {
          expect(LazyLoader.loadImage).toHaveBeenCalled();
          expect(newImg).toHaveClass('js-lazy-loaded');
          done();
        })
        .catch(done.fail);
    });
  });

  describe('with IntersectionObserver', () => {
    beforeEach(function() {
      loadFixtures('issues/issue_with_comment.html');

      lazyLoader = new LazyLoader({
        observerNode: 'foobar',
      });

      spyOn(LazyLoader, 'loadImage').and.callThrough();

      spyOn(window, 'requestAnimationFrame').and.callFake(execImmediately);
      spyOn(window, 'requestIdleCallback').and.callFake(execImmediately);

      // Doing everything that happens normally in onload
      lazyLoader.register();
    });

    afterEach(() => {
      lazyLoader.unregister();
    });

    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');

      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();
        })
        .catch(done.fail);
    });

    it('should lazy load dynamically added data-src images', function(done) {
      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.className = 'lazy';
      newImg.setAttribute('data-src', testPath);
      document.body.appendChild(newImg);

      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();
        })
        .catch(done.fail);
    });

    it('should not alter normal images', function(done) {
      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.setAttribute('src', testPath);
      document.body.appendChild(newImg);

      scrollIntoViewPromise(newImg)
        .then(waitForPromises)
        .then(() => {
          expect(LazyLoader.loadImage).not.toHaveBeenCalled();
          expect(newImg).not.toHaveClass('js-lazy-loaded');
          done();
        })
        .catch(done.fail);
    });

    it('should not load dynamically added pictures if content observer is turned off', done => {
      lazyLoader.stopContentObserver();

      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.className = 'lazy';
      newImg.setAttribute('data-src', testPath);
      document.body.appendChild(newImg);

      scrollIntoViewPromise(newImg)
        .then(waitForPromises)
        .then(() => {
          expect(LazyLoader.loadImage).not.toHaveBeenCalled();
          expect(newImg).not.toHaveClass('js-lazy-loaded');
          done();
        })
        .catch(done.fail);
    });

    it('should load dynamically added pictures if content observer is turned off and on again', done => {
      lazyLoader.stopContentObserver();
      lazyLoader.startContentObserver();

      const newImg = document.createElement('img');
      const testPath = `${TEST_HOST}/img/testimg.png`;
      newImg.className = 'lazy';
      newImg.setAttribute('data-src', testPath);
      document.body.appendChild(newImg);

      Promise.all([
        scrollIntoViewPromise(newImg),
        waitForAttributeChange(newImg, ['data-src', 'src']),
      ])
        .then(() => {
          expect(LazyLoader.loadImage).toHaveBeenCalled();
          expect(newImg).toHaveClass('js-lazy-loaded');
          done();
        })
        .catch(done.fail);
    });
  });
});