core(report): show nodeLabel for DOM nodes in addition to snippet

lighthouse-cli/test/smokehouse/seo/expectations.js

@@ -205,6 +205,7 @@ module.exports = [
                  '\n        too small target\n      </a>',
                   'path': '2,HTML,1,BODY,3,DIV,21,DIV,0,A',
                   'selector': 'body > div > div > a',
+                  'nodeLabel': 'too small target',
                 },
                 'overlappingTarget': {
                   'type': 'node',
@@ -213,6 +214,7 @@ module.exports = [
                   '\n        big enough target\n      </a>',
                   'path': '2,HTML,1,BODY,3,DIV,21,DIV,1,A',
                   'selector': 'body > div > div > a',
+                  'nodeLabel': 'big enough target',
                 },
                 'size': '100x30',
                 'width': 100,

lighthouse-core/audits/accessibility/axe-audit.js

@@ -54,6 +54,7 @@ class AxeAudit extends Audit {
           path: node.path,
           snippet: node.html || node.snippet,
           explanation: node.failureSummary,
+          nodeLabel: node.nodeLabel,
         }),
       }));
     }

lighthouse-core/audits/seo/tap-targets.js

@@ -251,6 +251,7 @@ function targetToTableNode(target) {
     snippet: target.snippet,
     path: target.path,
     selector: target.selector,
+    nodeLabel: target.nodeLabel,
   };
 }
 

lighthouse-core/gather/gatherers/accessibility.js

@@ -5,7 +5,7 @@
  */
 'use strict';
 
-/* global window, document, getOuterHTMLSnippet, getNodePath */
+/* global window, document, getOuterHTMLSnippet, getNodePath, getNodeLabel */
 
 const Gatherer = require('./gatherer');
 const fs = require('fs');
@@ -57,6 +57,8 @@ function runA11yChecks() {
       node.path = getNodePath(node.element);
       // @ts-ignore - getOuterHTMLSnippet put into scope via stringification
       node.snippet = getOuterHTMLSnippet(node.element);
+      // @ts-ignore - getNodeLabel put into scope via stringification
+      node.nodeLabel = getNodeLabel(node.element);
       // avoid circular JSON concerns
       node.element = node.any = node.all = node.none = undefined;
     }));
@@ -77,6 +79,7 @@ class Accessibility extends Gatherer {
     const expression = `(function () {
       ${pageFunctions.getOuterHTMLSnippetString};
       ${pageFunctions.getNodePathString};
+      ${pageFunctions.getNodeLabelString};
       ${axeLibSource};
       return (${runA11yChecks.toString()}());
     })()`;

lighthouse-core/gather/gatherers/seo/tap-targets.js

@@ -5,7 +5,7 @@
  */
 'use strict';
 
-/* global getComputedStyle, getElementsInDocument, Node, getNodePath, getNodeSelector */
+/* global getComputedStyle, getElementsInDocument, Node, getNodePath, getNodeSelector, getNodeLabel */
 
 const Gatherer = require('../gatherer');
 const pageFunctions = require('../../../lib/page-functions.js');
@@ -239,7 +239,7 @@ function elementIsPositionFixedStickyOrAbsolute(element) {
 /**
  * @param {string} str
  * @param {number} maxLength
- * @returns {string}
+ * @return {string}
  */
 /* istanbul ignore next */
 function truncate(str, maxLength) {
@@ -294,6 +294,8 @@ function gatherTapTargets() {
       path: getNodePath(tapTargetElement),
       // @ts-ignore - getNodeSelector put into scope via stringification
       selector: getNodeSelector(tapTargetElement),
+      // @ts-ignore - getNodeLabel put into scope via stringification
+      nodeLabel: getNodeLabel(tapTargetElement),
       href: /** @type {HTMLAnchorElement} */(tapTargetElement)['href'] || '',
     });
   });
@@ -323,6 +325,7 @@ class TapTargets extends Gatherer {
       ${rectContainsString};
       ${pageFunctions.getNodePathString};
       ${pageFunctions.getNodeSelectorString};
+      ${pageFunctions.getNodeLabelString};
       ${gatherTapTargets.toString()};
 
       return gatherTapTargets();

lighthouse-core/lib/page-functions.js

@@ -187,7 +187,7 @@ function getNodePath(node) {
 
 /**
  * @param {Element} node
- * @returns {string}
+ * @return {string}
  */
 /* istanbul ignore next */
 function getNodeSelector(node) {
@@ -218,6 +218,47 @@ function getNodeSelector(node) {
   return parts.join(' > ');
 }
 
+/**
+ * Generate a human-readable label for the given element, based on end-user facing
+ * strings like the innerText or alt attribute.
+ * Falls back to the tagName if no useful label is found.
+ * @param {HTMLElement} node
+ * @return {string|null}
+ */
+/* istanbul ignore next */
+function getNodeLabel(node) {
+  // Inline so that audits that import getNodeLabel don't
+  // also need to import truncate
+  /**
+   * @param {string} str
+   * @param {number} maxLength
+   * @return {string}
+   */
+  function truncate(str, maxLength) {
+    if (str.length <= maxLength) {
+      return str;
+    }
+    return str.slice(0, maxLength - 1) + '…';
+  }
+
+  const tagName = node.tagName.toLowerCase();
+  // html and body content is too broad to be useful, since they contain all page content
+  if (tagName !== 'html' && tagName !== 'body') {
+    const nodeLabel = node.innerText || node.getAttribute('alt') || node.getAttribute('aria-label');
+    if (nodeLabel) {
+      return truncate(nodeLabel, 80);
+    } else {
+      // If no useful label was found then try to get one from a child.
+      // E.g. if an a tag contains an image but no text we want the image alt/aria-label attribute.
+      const nodeToUseForLabel = node.querySelector('[alt], [aria-label]');
+      if (nodeToUseForLabel) {
+        return getNodeLabel(/** @type {HTMLElement} */ (nodeToUseForLabel));
+      }
+    }
+  }
+  return tagName;
+}
+
 module.exports = {
   wrapRuntimeEvalErrorInBrowserString: wrapRuntimeEvalErrorInBrowser.toString(),
   registerPerformanceObserverInPageString: registerPerformanceObserverInPage.toString(),
@@ -230,4 +271,6 @@ module.exports = {
   getNodePathString: getNodePath.toString(),
   getNodeSelectorString: getNodeSelector.toString(),
   getNodeSelector: getNodeSelector,
+  getNodeLabel: getNodeLabel,
+  getNodeLabelString: getNodeLabel.toString(),
 };

lighthouse-core/report/html/renderer/details-renderer.js

@@ -352,15 +352,24 @@ class DetailsRenderer {
    */
   renderNode(item) {
     const element = this._dom.createElement('span', 'lh-node');
+    if (item.nodeLabel) {
+      const nodeLabelEl = this._dom.createElement('div');
+      nodeLabelEl.textContent = item.nodeLabel;
+      element.appendChild(nodeLabelEl);
+    }
     if (item.snippet) {
-      element.textContent = item.snippet;
+      const snippetEl = this._dom.createElement('div');
+      snippetEl.classList.add('lh-node__snippet');
+      snippetEl.textContent = item.snippet;
+      element.appendChild(snippetEl);
     }
     if (item.selector) {
       element.title = item.selector;
     }
     if (item.path) element.setAttribute('data-path', item.path);
     if (item.selector) element.setAttribute('data-selector', item.selector);
     if (item.snippet) element.setAttribute('data-snippet', item.snippet);
+
     return element;
   }
 

lighthouse-core/report/html/report-styles.css

@@ -80,7 +80,8 @@
   --chevron-size: 12px;
   --inner-audit-left-padding: calc(var(--score-shape-size) + var(--score-shape-margin-left) + var(--score-shape-margin-right));
 
-  /* Palette. */
+  /* Palette using Material Design Colors
+   * https://www.materialui.co/colors */
   --color-black-100: #F5F5F5;
   --color-black-200: #E0E0E0;
   --color-black-400: #BDBDBD;
@@ -100,6 +101,8 @@
   --color-white: #FFFFFF;
   --color-blue-200: #90CAF9;
   --color-blue-900: #0D47A1;
+  --color-cyan-500: #00BCD4;
+  --color-teal-600: #00897B;
 
 
   /* TODO(cjamcl) clean up unused variables. */
@@ -175,6 +178,7 @@
 .lh-vars.dark {
   --color-red-700: var(--color-red);
   --color-green-700: var(--color-green);
+  --color-teal-600: var(--color-cyan-500);
   --color-orange-700: var(--color-orange);
 
   --color-black-200: var(--color-black-800);
@@ -388,10 +392,11 @@
 }
 
 /* Node */
-.lh-node {
-  display: block;
+.lh-node__snippet {
   font-family: var(--monospace-font-family);
-  color: hsl(174, 100%, 27%);
+  color: var(--color-teal-600);
+  font-size: 12px;
+  line-height: 1.5em;
 }
 
 /* Score */

lighthouse-core/test/lib/page-functions-test.js

@@ -59,4 +59,37 @@ describe('Page Functions', () => {
       assert.equal(pageFunctions.getNodeSelector(childEl), 'div#wrapper > div.child');
     });
   });
+
+  describe('getNodeLabel', () => {
+    it('Returns innerText if element has visible text', () => {
+      const el = dom.createElement('div');
+      el.innerText = 'Hello';
+      assert.equal(pageFunctions.getNodeLabel(el), 'Hello');
+    });
+
+    it('Falls back to children and alt/aria-label if a title can\'t be determined', () => {
+      const el = dom.createElement('div');
+      const childEl = dom.createElement('div', '', {'aria-label': 'Something'});
+      el.appendChild(childEl);
+      assert.equal(pageFunctions.getNodeLabel(el), 'Something');
+    });
+
+    it('Truncates long text', () => {
+      const el = dom.createElement('div');
+      el.setAttribute('alt', Array(100).fill('a').join(''));
+      assert.equal(pageFunctions.getNodeLabel(el).length, 80);
+    });
+
+    it('Uses tag name for html tags', () => {
+      const el = dom.createElement('html');
+      assert.equal(pageFunctions.getNodeLabel(el), 'html');
+    });
+
+    it('Uses tag name if there is no better label', () => {
+      const el = dom.createElement('div');
+      const childEl = dom.createElement('span');
+      el.appendChild(childEl);
+      assert.equal(pageFunctions.getNodeLabel(el), 'div');
+    });
+  });
 });