GoogleChrome · patrickhulce · Aug 24, 2021 · Jul 30, 2021 · Jul 31, 2021 · Jul 31, 2021
diff --git a/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap b/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
@@ -141,6 +141,9 @@ Object {
     Object {
       "path": "largest-contentful-paint-element",
     },
+    Object {
+      "path": "lcp-lazy-loaded",
+    },
     Object {
       "path": "layout-shift-elements",
     },
@@ -1092,6 +1095,11 @@ Object {
           "id": "largest-contentful-paint-element",
           "weight": 0,
         },
+        Object {
+          "group": "diagnostics",
+          "id": "lcp-lazy-loaded",
+          "weight": 0,
+        },
         Object {
           "group": "diagnostics",
           "id": "layout-shift-elements",

diff --git a/lighthouse-core/audits/lcp-lazy-loaded.js b/lighthouse-core/audits/lcp-lazy-loaded.js
@@ -0,0 +1,88 @@
+/**
+ * @license Copyright 2021 The Lighthouse Authors. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
+ */
+'use strict';
+
+const Audit = require('./audit.js');
+const i18n = require('../lib/i18n/i18n.js');
+
+const UIStrings = {
+  /** Descriptive title of a diagnostic audit that provides */
+  title: 'Largest Contentful Paint element was lazy-loaded',
+  /** Description of a Lighthouse audit that tells */
+  description: 'Consider to remove lazy loading for largest contentful paint element.',
+};
+
+const str_ = i18n.createMessageInstanceIdFn(__filename, UIStrings);
+
+class LargestContentfulPaintLazyLoaded extends Audit {
+  /**
+   * @return {LH.Audit.Meta}
+   */
+  static get meta() {
+    return {
+      id: 'lcp-lazy-loaded',
+      title: str_(UIStrings.title),
+      description: str_(UIStrings.description),
+      supportedModes: ['navigation'],
+      requiredArtifacts: ['TraceElements', 'ViewportDimensions', 'ImageElements'],
+    };
+  }
+
+  /**
+   * @param {LH.Artifacts.ImageElement} image
+   * @param {LH.Artifacts.ViewportDimensions} viewportDimensions
+   * @return {boolean}
+   */
+  static isImageInViewport(image, viewportDimensions) {
+    const imageTop = image.clientRect.top;
+    const viewportHeight = viewportDimensions.innerHeight;
+    return imageTop < viewportHeight;
+  }
+
+  /**
+   * @param {LH.Artifacts} artifacts
+   * @return {LH.Audit.Product}
+   */
+  static audit(artifacts) {
+    const images = artifacts.ImageElements;
+    const lazyLoadedImages = images.filter(
+      image => image.loading === 'lazy');
+    const lcpElement = artifacts.TraceElements
+      .find(element => element.traceEventType === 'largest-contentful-paint');
+
+    const lcpElementDetails = [];
+    if (lcpElement) {
+      const lcpImageElement = lazyLoadedImages.find(elem => {
+        return elem.node.devtoolsNodePath === lcpElement.node.devtoolsNodePath
+            && this.isImageInViewport(elem, artifacts.ViewportDimensions);
+      });
+      if (lcpImageElement) {
+        lcpElementDetails.push({
+          node: Audit.makeNodeItem(lcpImageElement.node),
+        });
+      }
+    }
+
+    if (lcpElementDetails.length === 0) {
+      return {score: 1, notApplicable: true};
+    }
+
+    /** @type {LH.Audit.Details.Table['headings']} */
+    const headings = [
+      {key: 'node', itemType: 'node', text: str_(i18n.UIStrings.columnElement)},
+    ];
+
+    const details = Audit.makeTableDetails(headings, lcpElementDetails);
+
+    return {
+      score: 0,
+      details,
+    };
+  }
+}
+
+module.exports = LargestContentfulPaintLazyLoaded;
+module.exports.UIStrings = UIStrings;
diff --git a/lighthouse-core/config/default-config.js b/lighthouse-core/config/default-config.js
@@ -229,6 +229,7 @@ const defaultConfig = {
     'third-party-summary',
     'third-party-facades',
     'largest-contentful-paint-element',
+    'lcp-lazy-loaded',
     'layout-shift-elements',
     'long-tasks',
     'no-unload-listeners',
@@ -466,6 +467,7 @@ const defaultConfig = {
         {id: 'third-party-summary', weight: 0, group: 'diagnostics'},
         {id: 'third-party-facades', weight: 0, group: 'diagnostics'},
         {id: 'largest-contentful-paint-element', weight: 0, group: 'diagnostics'},
+        {id: 'lcp-lazy-loaded', weight: 0, group: 'diagnostics'},
         {id: 'layout-shift-elements', weight: 0, group: 'diagnostics'},
         {id: 'uses-passive-event-listeners', weight: 0, group: 'diagnostics'},
         {id: 'no-document-write', weight: 0, group: 'diagnostics'},

diff --git a/lighthouse-core/lib/i18n/locales/en-US.json b/lighthouse-core/lib/i18n/locales/en-US.json
diff --git a/lighthouse-core/lib/i18n/locales/en-XL.json b/lighthouse-core/lib/i18n/locales/en-XL.json
diff --git a/lighthouse-core/test/audits/lcp-lazy-loaded-test.js b/lighthouse-core/test/audits/lcp-lazy-loaded-test.js
@@ -0,0 +1,62 @@
+/**
+ * @license Copyright 2020 The Lighthouse Authors. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
+ */
+'use strict';
+
+const LargestContentfulPaintLazyLoaded =
+  require('../../audits/lcp-lazy-loaded.js');
+
+/* eslint-env jest */
+describe('Performance: lcp-lazy-loaded audit', () => {
+  it('correctly surfaces the lazy loaded LCP element', async () => {
+    const node = {
+      devtoolsNodePath: '1,HTML,1,BODY,3,DIV,2,IMG',
+      selector: 'div.l-header > div.chorus-emc__content',
+      nodeLabel: 'My Test Label',
+      snippet: '<img class="test-class">',
+    };
+    const artifacts = {
+      TraceElements: [{
+        traceEventType: 'largest-contentful-paint',
+        node,
+      }],
+      ImageElements: [
+        {
+          src: 'test',
+          loading: 'lazy',
+          clientRect: {
+            top: 0,
+            bottom: 400,
+            left: 0,
+            right: 0,
+          },
+          node,
+        },
+      ],
+      ViewportDimensions: {
+        innerHeight: 500,
+        innerWidth: 300,
+      },
+    };
+
+    const auditResult = await LargestContentfulPaintLazyLoaded.audit(artifacts);
+    expect(auditResult.score).toEqual(0);
+    expect(auditResult.details.items).toHaveLength(1);
+    expect(auditResult.details.items[0].node.path).toEqual('1,HTML,1,BODY,3,DIV,2,IMG');
+    expect(auditResult.details.items[0].node.nodeLabel).toEqual('My Test Label');
+    expect(auditResult.details.items[0].node.snippet).toEqual('<img class="test-class">');
+  });
+
+  it('doesn\'t throw an error when there is nothing to show', async () => {
+    const artifacts = {
+      TraceElements: [],
+      ImageElements: [],
+    };
+
+    const auditResult = await LargestContentfulPaintLazyLoaded.audit(artifacts);
+    expect(auditResult.score).toEqual(1);
+    expect(auditResult.notApplicable).toEqual(true);
+  });
+});
diff --git a/lighthouse-core/test/fraggle-rock/api-test-pptr.js b/lighthouse-core/test/fraggle-rock/api-test-pptr.js
@@ -194,7 +194,7 @@ describe('Fraggle Rock API', () => {
       const {lhr} = result;
       const {auditResults, failedAudits, erroredAudits} = getAuditsBreakdown(lhr);
       // TODO(FR-COMPAT): This assertion can be removed when full compatibility is reached.
-      expect(auditResults.length).toMatchInlineSnapshot(`153`);
+      expect(auditResults.length).toMatchInlineSnapshot(`154`);
       expect(erroredAudits).toHaveLength(0);
 
       const failedAuditIds = failedAudits.map(audit => audit.id);

diff --git a/lighthouse-core/test/results/sample_v2.json b/lighthouse-core/test/results/sample_v2.json
@@ -1859,6 +1859,13 @@
         ]
       }
     },
+    "lcp-lazy-loaded": {
+      "id": "lcp-lazy-loaded",
+      "title": "Largest Contentful Paint element was lazy-loaded",
+      "description": "Consider to remove lazy loading for largest contentful paint element.",
+      "score": null,
+      "scoreDisplayMode": "notApplicable"
+    },
     "layout-shift-elements": {
       "id": "layout-shift-elements",
       "title": "Avoid large layout shifts",
@@ -5188,6 +5195,11 @@
           "weight": 0,
           "group": "diagnostics"
         },
+        {
+          "id": "lcp-lazy-loaded",
+          "weight": 0,
+          "group": "diagnostics"
+        },
         {
           "id": "layout-shift-elements",
           "weight": 0,
@@ -6352,6 +6364,12 @@
         "duration": 100,
         "entryType": "measure"
       },
+      {
+        "startTime": 0,
+        "name": "lh:audit:lcp-lazy-loaded",
+        "duration": 100,
+        "entryType": "measure"
+      },
       {
         "startTime": 0,
         "name": "lh:audit:layout-shift-elements",
@@ -7691,6 +7709,12 @@
         "audits[non-composited-animations].details.headings[0].text",
         "audits[dom-size].details.headings[1].text"
       ],
+      "lighthouse-core/audits/lcp-lazy-loaded.js | title": [
+        "audits[lcp-lazy-loaded].title"
+      ],
+      "lighthouse-core/audits/lcp-lazy-loaded.js | description": [
+        "audits[lcp-lazy-loaded].description"
+      ],
       "lighthouse-core/audits/layout-shift-elements.js | title": [
         "audits[layout-shift-elements].title"
       ],