viewport.js

/**
 * @license
 * Copyright 2016 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import {Audit} from './audit.js';
import {ViewportMeta} from '../computed/viewport-meta.js';
import * as i18n from '../lib/i18n/i18n.js';

const UIStrings = {
  /** Title of a Lighthouse audit that provides detail on the viewport meta tag in a web page's html. This descriptive title is shown to users when a viewport tag is set and configured. */
  title: 'Has a `<meta name="viewport">` tag with `width` or `initial-scale`',
  /** Title of a Lighthouse audit that provides detail on the viewport meta tag in a web page's html. This descriptive title is shown to users when a viewport tag is not set or configured. */
  failureTitle: 'Does not have a `<meta name="viewport">` tag with `width` ' +
    'or `initial-scale`',
  /** Description of a Lighthouse audit that tells the user why they should have a viewport meta tag in their html. 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: 'A `<meta name="viewport">` not only optimizes your app for mobile screen sizes, ' +
    'but also prevents [a 300 millisecond delay to user input](https://developer.chrome.com/blog/300ms-tap-delay-gone-away/). ' +
    '[Learn more about using the viewport meta tag](https://developer.chrome.com/docs/lighthouse/pwa/viewport/).',
  /** Explanatory message stating that no viewport meta tag exists on the page. */
  explanationNoTag: 'No `<meta name="viewport">` tag found',
};

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

class Viewport extends Audit {
  /**
   * @return {LH.Audit.Meta}
   */
  static get meta() {
    return {
      id: 'viewport',
      title: str_(UIStrings.title),
      failureTitle: str_(UIStrings.failureTitle),
      description: str_(UIStrings.description),
      guidanceLevel: 3,
      requiredArtifacts: ['MetaElements'],
      scoreDisplayMode: Audit.SCORING_MODES.METRIC_SAVINGS,
    };
  }

  /**
   * @param {LH.Artifacts} artifacts
   * @param {LH.Audit.Context} context
   * @return {Promise<LH.Audit.Product>}
   */
  static async audit(artifacts, context) {
    const viewportMeta = await ViewportMeta.request(artifacts.MetaElements, context);

    let inpSavings = 300;
    if (!viewportMeta.hasViewportTag) {
      return {
        score: 0,
        explanation: str_(UIStrings.explanationNoTag),
        metricSavings: {
          INP: inpSavings,
        },
      };
    }

    if (viewportMeta.isMobileOptimized) {
      inpSavings = 0;
    }

    /** @type {LH.Audit.Details.DebugData|undefined} */
    let details;
    if (viewportMeta.rawContentString !== undefined) {
      details = {
        type: 'debugdata',
        viewportContent: viewportMeta.rawContentString,
      };
    }

    return {
      score: Number(viewportMeta.isMobileOptimized),
      metricSavings: {
        INP: inpSavings,
      },
      warnings: viewportMeta.parserWarnings,
      details,
    };
  }
}

export default Viewport;
export {UIStrings};