Skip to content


JavaScript library to help modern web applications with accessibility concerns by making accessibility simpler

# Utilities

the util infrastructure does not contain any functionality relevant to a user of ally.js. It merely contains code supporting other components, e.g. to ensure consistent component function signatures for a consistent APIs. To be honest, it's also the dumping ground for everything that didn't fit into one of the other buckets. None of these functions are available through the ally object exposed by the production file dist/ally.min.js, but are very much accessible via modules.

# Contributing

# Platform

In order to make using platform.js even simpler, this utility adds the few verifications ally.js actually needs.

# Logger

In order to safely access - and in the future possibly mutate - any calls to console.log et al, we're importing the logger utility, rather than referencing console.* directly.

# Translate input to node array

Internally ally.js prefers to use Arrays of Nodes, but when accepting input from the outside we're not sure what we get. NodeList, HTMLCollection, jQuery object, a single Node or even just a string (to run through document.querySelectorAll) - util/node-array.js converts everything to array.

# Context to element

util/context-to-element.js is an internal convenience function to hide grabbing the first element of util/node-array or throwing an TypeError if nothing was found. It is unclear if this "convenience" may cause developers to complain about indirected stack traces.

# Decorate service

util/decorate-service.js is a decorator wrapping a component's setup (engage) and teardown (disengage) functions in a way that exposes the component with the following trivialized signature:

function engage() {
  return {
    disengage: function() {

The "service" aspect here is that a components engage() function can be invoked from anyone anywhere anytime without having to track if the component has already been initialized before. This is made possible by a simple reference counter. If three components engage() but only two disengage(), the component.disengage() is never executed. Only after the last reference has been disengage()d, the component is told to teardown. It is possible to force teardown by executing disengage({force: true}).

A component's engage() function may return an result object. The decorated disengage() function is added to that result object, returned to the caller and cached for subsequent calls to the decorated engage() function.

# Decorate options.context

util/decorate-context is a decorate wrapping a component's setup (engage()) and teardown (disengage()) functions in a way that exposes the component with the following trivialized signature:

function engage(options) {
  var context = nodeArray(options.context);
  context.forEach(function(element) {
  return {
    disengage: function() {
      context.forEach(function(element) {

Unlike the singleton decorator, the context decorator allows multiple concurrent instances of a component. There is no need for counting references - disengage()ing is the library user's obligation.

A component's engage() function may return an result object. The decorated disengage() function is added to that result object and returned to the caller. Unlike the singleton decorator, the context decorator returns a unique result object for every engage() invocation.

# Sort elements according to DOM order

util/sort-dom-order sorts an Array of elements according to their relative position in the DOM.

# Merge elements according to DOM order

util/merge-dom-order merges an Array of elements with another Array of elements so that the resulting array's sorting order corresponds to DOM each element's relative position in the DOM.

# Retrieve tabindex value

util/tabindex-value returns the value of the tabindex attribute (not property!) as an integer, or null for missing or invalid values

# Calculate an element's visible area

util/visible-area calculates the fraction of the area that is visible in the viewport (1 fully visible, 0 not visible at all, 0.5 half the element is visible, the rest is hidden by scroll containers)

# Compare document position

util/compare-position provides utilities for comparing the relative position of elements in the DOM for use with higher order functions (such as

# Toggle attribute value

util/toggle-attribute-value can will change an attribute's value, while saving its former value to allow restoring the previous state

# Select in ShadowDOM

util/select-in-shadows mutates a given CSS selector in order to make it match elements in ShadowDOM as well.

# Get a Node's document, window and content document

# Mutate Element.className (classList)

util/toggle-class mutates a given element's class attribute without using classList, as this is not consistently available on Element and SVGEelement.

# Reset scroll positions

util/reset-scrolling collects the scroll positions of the given element's ancestors. The function returned as a result will reset the elements to the collected elements' positions. This is useful to revert the effect of an operation that causes unpreventable scrolling.

# Match element agains CSS selector

util/element-matches provides a simple interface to using Element.matches through its various vendor-prefixed names.

# Find an item in an array

util/array-find-index is a simple wrapper that provides the same functionality as Array.findIndex for non ES 6 browsers.