HTML best practices
Structuring code and navigation
Think of code hierarchy when structuring your content so that screen readers and keyboard-only users can access interactive elements in a logical and predictable order via tabbing. Create the tab flow hierarchy by using the source code to arrange the keyboard navigation. Begin with the header, followed by the main navigation, then page navigation (from left to right, top to bottom), and end with the footer. The objective is to give keyboard users an intentional experience that is comparable to the experience of mouse users.
Use semantic HTML
Use native HTML elements as much as you can and use them for their correct purpose. These elements have built-in accessibility benefits. They inform screen readers what they are and do, and standard interactive elements, such as button, include keyboard functionality. Aside from making it accessible, this will also make it easier to develop and maintain, better on mobile and good for SEO.
<button>Play Video</button>
<header></header>
<main></main>
<nav></nav>
<footer></footer>
<aside></aside>
<section></section>
<article></article>
Use clear language
When adding content, consider cognitive disabilities, younger people or early readers who may access your site, anyone whose native language isn’t the language your content is written in, and screen readers. Avoid dashes, abbreviations, acronyms (at least the first time) and table layouts if a table is not needed. If abbreviating, use native <abbr /> element with title attribute.
"9 to 5"
"November"
<abbr title='November'>Nov</abbr>
Use meaningful text labels
Consider visually impaired people when labeling elements. Make sure there is textual context for screen readers.
<!-- Do this -->
<a>Read more about pricing</a>
<!-- Not this -->
<a>Click here</a>
Making accessible data tables
Always specify table headers with <th /> elements, and make sure they stand out. Utilize scope attribute if necessary to specify if they are headers for rows or columns. Utilize alternative text along with tables for visually impaired users. <caption /> is preferred, but <table /> summary works, too.
<table summary='Names and Ages of My Coworkers'>
<caption>Names and Ages of My Coworkers</caption>
<thead>
<tr>
<th scope="col">Firstname</th>
<th scope="col">Lastname</th>
<th scope="col">Age</th>
</tr>
</thead>
<tbody>
<tr>
<td>Jane</td>
<td>Smith</td>
<td>22</td>
</tr>
<tr>
<td>Tom</td>
<td>West</td>
<td>47</td>
</tr>
</tbody>
</table>
Making accessible data visualizations
It is important to take into account visually impaired users when including data visualizations. Consider accompanying visuals with a data table is another alternative for users who rely on screen readers. It is also important to take into account color choices for color-blind users.
Multimedia text alternatives
Every image that is not decorative must include alt text with a meaningful description of the image and a title attribute. You can also utilize aria-labelledby along with id attributes instead of alt text. If the image is decorative, use an empty alt attribute, otherwise the screen reader will read the whole image url if the alt is left out.
<!-- Example 1 -->
<img src='puppy.jpg' title='Sleeping Puppy' alt='A sleeping puppy'/>
<!-- Example 2 -->
<img src='puppy2.jpg' aria-labelledby='imagelabel'/>
<p id='imagelabel'>This is a picture of a cute puppy in cup</p>
Audio alternatives
Provide closed-captioning with videos or transcriptions of audio files.
<video controls>
<source src='example.mp4' type='video/mp4'/>
<source src='example.webm' type='video/webm'/>
<track kind='subtitles' src='subtitles_english.vtt' srclang='en'/>
</video>
Avoid font icon libraries
Use SVG's instead of font icon libraries as those are not accessible.
<svg width="80" height="10">
<line class='line' x1="200" y1="0" x2="0" y2="0" />
</svg>
Utilize ARIA (Accessible Rich Internet Application) roles and landmark roles
ARIA roles convey the intent or meaning of an element to assistive technology. This helps users navigate when they can't see the layout and provides further context about different functionalities.
Landmark roles identify regions in a page, and act much like native HTML tags would when it comes to semantics. Signpost roles describe other information about a given element's functionality on a page. These are especially helpful when building complex, custom interfaces or to reinforce semantics in native HTML elements.
<!-- landmark roles -->
<nav role='navigation'></nav>
<main role='main'></main>
<!-- signpost roles -->
<div role='banner'>This is a banner.</div>
<div role='tabgroup'>
<div role='tab'></div>
</div>
<div role='combobox'></div>
<div role='slider'></div>
<button role='button'></button>
CSS best practices
CSS rule of thumb
You can style a page feature to fit your design but don't change it to the point that it doesn't look or behave as expected. Just because you can use CSS to make any HTML element to look like anything doesn't mean that you should.
Style focus indicators
Add styling to tabbable elements on hover and focus, so that keyboard only users can have a clear visual of where they are navigating. Never suppress the focus indicator altogether.
Hiding elements
When hiding content from a screen reader, consider source order. Use visibility: hidden, along with display: none in your CSS.
JS best practices
JavaScript rule of thumb
Don't rely too much on JavaScript to generate HTML and CSS. Follow the "Unobtrusive JavaScript" principle, which means that JavaScript should be used to enhance functionality not build it entirely. Use your built-in browser functionality as much as possible. If you're utilizing JavaScript to make complex UI features, use WAI-ARIA to make elements accessible. Examples of unobtrusive JavaScript include providing client-side form validation and custom controls for HTML5 <video /> elements that are accessible to keyboards.
Accessible mouse specific events
Double up mouse specific events with other events for keyboard only users.
const foo = document.querySelector('.foo-class');
foo.onmouseover = someFunction();
foo.onmouseout = anotherFunction();
foo.onfocus = someFunction();
foo.onblur = anotherFunction();