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aria.js

An HTMLElement wrapper to make setting and evaluating ARIA attributes easier.

Motivation

ARIA attributes add semantics to HTML elements and thus improve interoperability with e.g. screen readers. This makes is possible (or at least easier) for blind people to use Web Apps.

Styling web applications for sighted people on the other hand is usually done with CSS classes. In contrast to ARIA attributes, they do not add semantics to the HTML elements.

As pointed out in the WAI-ARIA Authoring Practices, "you should consider binding user interface changes directly to changes in WAI-ARIA states and properties, such as through the use of CSS attribute selectors." That means you can use ARIA attributes for both, semantics and styling. People actually do this, ebay developers for example based their CSS framework on this idea (see "How Our CSS Framework Helps Enforce Accessibility", a great resource to read).

And here is the point: While classList made it super easy to deal with CSS classes, there is no supporting API for ARIA attributes.

A straight-forward approach would be to add properties to HTMLElement objects which correspond to the ARIA attributes, e.g.:

element.ariaHidden = true; // sets the aria-hidden attribute to true

The aria.js wrapper is as close as possible to this idea:

aria(element).hidden = true;

In contrast to Element.getAttribute()/setAttribute(), aria.js is typed:

assert(element.getAttribute('hidden') === 'true');
assert(aria(element).hidden === true); // boolean

assert(element.getAttribute('activedescendant') === 'my-sub-element');
assert(aria(element).activedescendant === document.getElementById('my-sub-element')); // HTMLElement

All attributes in the current specs are supported. Have a look at the tests for the details.

Usage

// get attribute aria-hidden
var hidden = aria(element).hidden;

// set attribute
aria(element).hidden = true;

// remove attribute by assigning null
aria(element).hidden = null;

Calling aria() all the time instead of storing the aria instance somewhere is actually cheap: The instance is cached on the element object.

You can also call aria() with an element ID instead of the element itself:

aria('my-element').hidden = true;

Error handling

aria(element).hidden = 'invalid value'; // is ignored

element.setAttribute('aria-hidden', 'invalid value');
hidden = aria(element).hidden; // returns false (the default value)

Adapting attribute getter or setter, adding new attributes

If you want to adapt the getter or setter of a certain attribute or need to add a new one, you have to add a corresponding property on aria.attributes. An example:

aria.attributes.hidden = { // definition of the "aria-hidden" getter and setter
    get: (attributeValue) => { // adjust the attribute value to the specific type
        if (attributeValue == 'true')
            return true;
        if (attributeValue == 'false' || attributeValue == null)
            return false; // Return the default value for null

        // throw a TypeError for an illegal value
        throw new TypeError('"' + attributeValue + '" is not true/false');
    },
    set: (value) => { // convert the value to a string which is set as attribute
        return Boolean(value).toString();
    }
};

TODOs

  • A strict mode for error handling
  • An npm package