lighthouse/core/audits/accessibility/color-contrast.js

Automated auditing, performance metrics, and best practices for the web.

/**
 * @license
 * Copyright 2017 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @fileoverview Ensures the contrast between foreground and background colors meets
 * WCAG 2 AA contrast ratio thresholds.
 * See base class in axe-audit.js for audit() implementation.
 */

import AxeAudit from './axe-audit.js';
import * as i18n from '../../lib/i18n/i18n.js';

const UIStrings = {
  /** Title of an accesibility audit that evaluates if all foreground colors are distinct enough from their background colors to be legible for users. This title is descriptive of the successful state and is shown to users when no user action is required. */
  title: 'Background and foreground colors have a sufficient contrast ratio',
  /** Title of an accesibility audit that evaluates if all foreground colors are distinct enough from their background colors to be legible for users. This title is descriptive of the failing state and is shown to users when there is a failure that needs to be addressed. */
  failureTitle: 'Background and foreground colors do not have a ' +
      'sufficient contrast ratio.',
  /** Description of a Lighthouse audit that tells the user *why* they should try to pass. This is displayed after a user expands the section to see more. No character length limits. The last sentence starting with 'Learn' becomes link text to additional documentation. */
  description: 'Low-contrast text is difficult or impossible for many users to read. ' +
      '[Learn how to provide sufficient color contrast](https://dequeuniversity.com/rules/axe/4.10/color-contrast).',
};

const str_ = i18n.createIcuMessageFn(import.meta.url, UIStrings);

class ColorContrast extends AxeAudit {
  /**
   * @return {LH.Audit.Meta}
   */
  static get meta() {
    return {
      id: 'color-contrast',
      title: str_(UIStrings.title),
      failureTitle: str_(UIStrings.failureTitle),
      description: str_(UIStrings.description),
      requiredArtifacts: ['Accessibility'],
    };
  }
}

export default ColorContrast;
export {UIStrings};