pwa-helpers/axe-report.js

/**
@license
Copyright (c) 2018 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
*/
/**
  This is an [axe-core](https://github.com/dequelabs/axe-core) reporter that returns an
  Error containing every a11y violation for an element. Use this if you want to
  include `axe-core` in automated Mocha tests, etc. Note that this helper does not
  include `axe-core` for you; you must do this separately.

  The `axeReport` function takes an optional second argument:
  {cleanup: {...}, axeConfig: {...}}, where `cleanup` is a callback to be
  called after the test is ran (so that you can remove the element from the DOM, etc)
  and `axeConfig` are the optional extra config parameters to pass to axe.

  Example (in a Mocha test):

      import 'axe-core/axe.min.js';
      import { axeReport } from 'pwa-helpers/axe-report.js';

      describe('button', function() {

        it('is accessible', function() {
          const button = document.createElement('button');
          button.textContent = 'click this'; // Test should fail without this line.
          return axeReport(button);

          // If you need to run any cleanup code after the test is run, you
          // can use the `cleanup` object. For example,
          // document.body.appendChild(button);
          // return axeReport(el, { cleanup() { el.remove(); } });
        });
      });
*/
export async function axeReport(dom, config = {}) {
    const { cleanup, axeConfig } = config;
    const defaultConfig = {
        runOnly: {
            type: 'tag',
            values: ['wcag2a', 'wcag2aa', 'section508']
        },
        // Ignore tests that are passing.
        resultTypes: ['violations']
    };
    const { violations } = await axe.run(dom, axeConfig || defaultConfig);
    if (cleanup) {
        await cleanup();
    }
    if (!violations.length) {
        return;
    }
    const errorMessage = ['Accessibility Violations', '---'];
    for (const violation of violations) {
        errorMessage.push(violation.help);
        for (const node of violation.nodes) {
            if (node.failureSummary) {
                errorMessage.push(node.failureSummary);
            }
            errorMessage.push(node.html);
        }
        errorMessage.push('---');
    }
    throw new Error(errorMessage.join('\n'));
}
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