Accessibility Developer Tools

This is a library of accessibility-related testing and utility code.

Its main component is the accessibility audit: a collection of audit rules checking for common accessibility problems, and an API for running these rules in an HTML page.

There is also a collection of accessibility-related utility code, including but not limited to:

• contrast ratio calculation and color suggestions
• retrieving and validating ARIA attributes and states
• accessible name calculation using the algorithm at http://www.w3.org/TR/wai-aria/roles#textalternativecomputation

Getting the code

To include just the javascript rules, require the following file:

https://raw.github.com/GoogleChrome/accessibility-developer-tools/stable/dist/js/axs_testing.js

git 1.6.5 or later:

% git clone --recursive https://github.com/GoogleChrome/accessibility-developer-tools.git

Before git 1.6.5:

% git clone https://github.com/GoogleChrome/accessibility-developer-tools.git
% cd accessibility-developer-tools
% git submodule init; git submodule update

Building

You will need node and grunt-cli to build.

1. (Once only) Install Node.js and npm - useful instructions here: https://gist.github.com/isaacs/579814

   Make sure you have Node.js v 0.8 or higher.

2. (Once only) Use npm to install grunt-cli

    % npm install -g grunt-cli  # May need to be run as root
   

3. (Every time you make a fresh checkout) Install dependencies (including grunt) for this project (run from project root)

    % npm install
   

4. Build using grunt (run from project root)

    % grunt
   

Using the Audit API

Including the library

The simplest option is to include the generated axs_testing.js library on your page.

Work is underway to include the library in WebDriver and other automated testing frameworks.

The axs.Audit.run() method

Once you have included axs_testing.js, you can call call axs.Audit.run(). This returns an object in the following form:

{
  /** @type {axs.constants.AuditResult} */
  result,  // one of PASS, FAIL or NA

  /** @type {Array.<Element>} */
  elements,  // The elements which the rule fails on, if result == axs.constants.AuditResult.FAIL

  /** @type {axs.AuditRule} */
  rule  // The rule which this result is for.
}

Command Line Runner

The Accessibility Developer Tools project includes a command line runner for the audit. To use the runner, install phantomjs then run the following command from the project root directory.

$ phantomjs tools/runner/audit.js <url-or-filepath>

The runner will load the specified file or URL in a headless browser, inject axs_testing.js, run the audit and output the report text.

Using the results

Interpreting the result

The result may be one of three constants:

• axs.constants.AuditResult.PASS - This implies that there were elements on the page that may potentially have failed this audit rule, but they passed. Congratulations!
• axs.constants.AuditResult.NA - This implies that there were no elements on the page that may potentially have failed this audit rule. For example, an audit rule that checks video elements for subtitles would return this result if there were no video elements on the page.
• axs.constants.AuditResult.FAIL - This implies that there were elements on the page that did not pass this audit rule. This is the only result you will probably be interested in.

Creating a useful error message

The static, global axs.Audit.createReport(results, opt_url) may be used to create an error message using the return value of axs.Audit.run(). This will look like the following:

*** Begin accessibility audit results ***
An accessibility audit found 4 errors and 4 warnings on this page.
For more information, please see https://github.com/GoogleChrome/accessibility-developer-tools/wiki/Audit-Rules

Error: badAriaAttributeValue (AX_ARIA_04) failed on the following elements (1 - 3 of 3):
DIV:nth-of-type(3) > INPUT
DIV:nth-of-type(5) > INPUT
#aria-invalid

Error: badAriaRole (AX_ARIA_01) failed on the following element:
DIV:nth-of-type(11) > SPAN

Error: controlsWithoutLabel (AX_TEXT_01) failed on the following elements (1 - 3 of 3):
DIV > INPUT
DIV:nth-of-type(12) > DIV:nth-of-type(3) > INPUT
LABEL > INPUT

Error: requiredAriaAttributeMissing (AX_ARIA_03) failed on the following element:
DIV:nth-of-type(13) > DIV:nth-of-type(11) > DIV

Warning: focusableElementNotVisibleAndNotAriaHidden (AX_FOCUS_01) failed on the following element:
#notariahidden

Warning: imagesWithoutAltText (AX_TEXT_02) failed on the following elements (1 - 2 of 2):
#deceptive-img
DIV:nth-of-type(13) > IMG

Warning: lowContrastElements (AX_COLOR_01) failed on the following elements (1 - 2 of 2):
DIV:nth-of-type(13) > DIV
DIV:nth-of-type(13) > DIV:nth-of-type(3)

Warning: nonExistentAriaLabelledbyElement (AX_ARIA_02) failed on the following elements (1 - 2 of 2):
DIV:nth-of-type(3) > INPUT
DIV:nth-of-type(5) > INPUT
*** End accessibility audit results ***

Each rule will have at most five elements listed as failures, in the form of a unique query selector for each element.

Configuring the Audit

If you wish to fine-tune the audit, you can create an axs.AuditConfiguration object, with the following options:

Ignore parts of the page for a particular audit rule

For example, say you have a separate high-contrast version of your page, and there is a CSS rule which causes certain elements (with class pretty) on the page to be low-contrast for stylistic reasons. Running the audit unmodified produces results something like

Warning: lowContrastElements (AX_COLOR_01) failed on the following elements (1 - 5 of 15):
...

You can modify the audit to ignore the elements which are known and intended to have low contrast like this:

var configuration = new axs.AuditConfiguration();
configuration.ignoreSelectors('lowContrastElements', '.pretty');
axs.Audit.run(configuration);

The AuditConfiguration.ignoreSelectors() method takes a rule name, which you can find in the audit report, and a query selector string representing the parts of the page to be ignored for that audit rule. Multiple calls to ignoreSelectors() can be made for each audit rule, if multiple selectors need to be ignored.

Restrict the scope of the entire audit to a subsection of the page

You may have a part of the page which varies while other parts of the page stay constant, like a content area vs. a toolbar. In this case, running the audit on the entire page may give you spurious results in the part of the page which doesn't vary, which may drown out regressions in the main part of the page.

You can set a scope on the AuditConfiguration object like this:

var configuration = new axs.AuditConfiguration();
configuration.scope = document.querySelector('main');  // or however you wish to choose your scope element
axs.Audit.run(configuration);

License

Copyright 2013 Google Inc. 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.