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An inline JavaScript accessibility widget dynamically served via single <script> tag, as obtained from API request to separate WCASG Dashboard app.


App Architecture

  • Typescript: Improved syntax and type checking.
  • Preact: A smaller footprint version of React that provides 90% of the functionality.
  • Redux: State management for use with Preact components.
  • SASS: Advanced styling.
  • Webpack + Babel: General tooling to generate final build UMD output.

Widget Theme

Widget theming provides an easy way to customize the look and feel of the widget with just a few palette color changes, or a total overhaul of element behavior and styling. Existing themes can be found in the src/theme directory. The base theme is the default Widget theme, based on design mockups.

Adding a New Theme

  1. Create a new directory in src/theme.
  2. Copy an existing theme index.ts and palette.ts into the new directory.
  3. Modify the new palette.ts colors constant as needed:
const colors = {
  background: '#fff',
  backgroundEnabled: '#FAFAFA',
  border: fade('#999999', 0.5),
  primary: '#297FCA',
  primaryDark: '#184570',
  primaryLight: '#e8f6ff',
  switchMain: '#fff',
  textSecondary: '#fff'
  1. Add a new entry to the ThemeTypes enum to identify your theme.
  2. Lastly, update the index.tsx theme section by importing your theme index file and adding it to the theme switch statement matching your new ThemeTypes entry.

Now invoke ActionCreators.setTheme({ theme: ThemeTypes.NewThemeType }) anywhere you wish to dispatch an action to update the theme. This will disperse the set theme to all Widget components and rerender.

Editing the Widget

The WCASG ADA Widget is constructed out of individual plugins, each of which can be toggled independently. Plugins are designed to be as modular as possible, to make it easier to add more functionality/plugins in the future.

A PluginElement handles the "view" and "state" of a given plugin. The PluginElement contains one or more child PluginActions that perform the actual DOM manipulation tasks relevant to that PluginElement.


At present, a PluginElement has the following basic properties:

export enum PluginElementType {

export interface IPluginElement {
  id?: string;
  name?: string;
  title?: string;
  type: PluginElementType;
  // Actions only trigger when enabled.
  enabled?: boolean;
  // Display order
  order?: number;
  // If excluded use default based on type.
  template?: (self?: any) => any;
  // Children are enabled if parent is enabled.
  children?: IPluginElement[];
  // Actions to execute
  actions?: IPluginActionTypes;
  // Get the current or default state object
  getInstanceState: (params?: any) => any;

A new PluginElement instance can be passed many of the above arguments to change its behavior. In addition to typing via Typescript, there are child classes that inherit from PluginElement that are designed for more specific tasks. For example, the PluginElementToggleable element creates a plugin that allows for enabling/disabling its PluginAction(s). The PluginElementScalable plugin is used for scaling or incremental actions.

The PluginElementSelectable and PluginElementMultiselectable elements are still incomplete, but will add explicit ability to work with multi-option states.


As mentioned, a PluginAction is a stateless instance that is a child of a given PluginElement. When the PluginElement dispatches a relevant state change it triggers its child PluginActions, which perform their assigned task (usually, updating the DOM).

As with PluginElements there are a few inherited PluginAction classes that perform explicit types of actions.

  • PluginActionClass alters a node's assigned CSS classes list, making it ideal for PluginElements that want to affect styling of the entire page.
  • PluginActionStyle is used for fine-grained manipulation of node styling. It is best used when modifying styling incrementally (such as font-size via the PluginElementScalable element).
  • PluginActionProperty alters the properties of the node (i.e. node[propertyName] = newValue).
  • PluginActionFunction is used for arbitrary function execution and should be constructed by passing one or more functions it will execute to the .func property.

In most cases, a PluginAction affects the DOM by altering relevant nodes (i.e. elements).

Adding or Modifying Plugins

A PluginElement is rendered to the DOM via its template property, which returns a JSX element that is rendered to the DOM via Preact. While PluginElements have a predefined template that is the default for all elements of that type, a custom template can be provided to change the look and behavior. For example, here is the current instantiation of the Adjust Font Size PluginElement:

export const pluginFontSize = new PluginElementScalable({
  title: 'Adjust Font Size',
  scalingIncrement: 0.1,
  actions: [
    new PluginActionStyle({
      name: 'adjust-font-size-action',
      style: {
        name: 'font-size',
        manipulationType: ValueManipulationType.PercentageScaling
      query: new TextNodeType().types.join(', ')

Many of the default arguments are fine, but the important change to PluginElementScalable is the scalingIncrement property is set to 0.1. The single action passed of PluginActionStyle is set to manipulate the font-size CSS property, and is given a manipulationType of PercentageScaling. In tandem, the scalingIncrement and the manipulationType will cause the font size of applicable nodes to be scaled by 10% (0.1 with a percentage scaling type) per adjustment. The only other option is the query property of the PluginAction, which defines the CSS query the plugin uses to collect nodes to be updated. In this case a predefined collection of text-based node names (e.g. a, span, etc) are passed.

The template property of PluginElementScalable can be seen here, but it basically displays some buttons to toggle the plugin, as well as adjust the scaling. However, if you wanted to explicitly override the template with something of your own you can do so in the element constructor, like so:

new PluginElementScalable({
  title: 'Adjust Font Size',
  scalingIncrement: 0.1,
  actions: [
    new PluginActionProperty({
      name: 'adjust-font-size-action',
      style: {
        name: 'font-size',
        manipulationType: ValueManipulationType.PercentageScaling
      node: new TextNodeType().types
  template: (self: any) => {
    const dispatch = useDispatch();

    const selectEnabled = useMemo(makeElementEnabledSelector, []);
    const enabled = useSelector(state => selectEnabled(state,;

    const selectScalingFactor = useMemo(makeElementScalingFactorSelector, []);
    const scalingFactor = useSelector(state =>

    useEffect(() => {
      const currentState = self.getInstanceState();
      const newState = self.getInstanceState({ enabled, scalingFactor });
      if (scalingFactor !== self.scalingFactor) {
        self.scalingFactor = scalingFactor;
      if (enabled !== self.enabled) {
        self.enabled = enabled;

      // Update on change
      if (!isEqual(currentState, newState)) {

    const handleToggleClick = () => {
        type: 'toggle',
        payload: { id: }

    const handleScaling = (): any => {
      const adjustment = document.getElementById('adjustment-slider').value;
        type: 'scale',
        payload: { id:, adjustment }

    return (
        className={`${styles['plugin-element']} ${styles['plugin-element-scalable']}`}
        <h3>A CUSTOM SLIDER!!!</h3>
        <p>Rounded Value: {Math.round(scalingFactor)}</p>
        <button type={'button'} onClick={() => handleToggleClick()}>
          {enabled ? 'Disable' : 'Enable'}
          onChange={() => handleScaling()}

Just about any valid JSX template can be generated and returned by the template property. The only requirement is to ensure all references to this now reference the self, which will assigned the parent PluginElement instance during render.

Other properties that can be changed to affect behavior include:

  • scalingFactor: This is the initial scaling value to apply. For example, if you wish to always increase font-size to 200% you'd set scalingFactor to an initial value of 1 and ensure the relevant PluginAction has a Percentage scaling type.
  • enabled: Determines if the plugin loads on or off.
  • order: Adjusts the visual ordering of plugins in the UI. (TODO)
  • getInstanceState: If you wish to add more stateful behavior beyond the default stuff included, start by altering the getInstanceState function and setting it to the base values for the element. See below for more on changing state.

Customizing Actions

An element can house one or more actions, each of which will be fired when the parent PluginElement is enabled or statefully-adjusted. Altering the behavior of different PluginAction types will change the way the DOM is manipulated when the action fires.

A PluginActionClass action accepts just a couple properties, namely:

  • klass: A string or Array<string> that indicates which classes will be added by the action when enabled. These values can already exist in the styling, or be explicitly imported from a .scss sheet.
  • query: A string that collects DOM nodes using the document.querySelectorAll method. For example, setting query: 'a, p, h1' will generate a collection of all links, paragraphs, and top-level headers in the DOM. When the action is enabled, the classes defined in klass will be applied to those nodes.

In many cases directly changing query is unnecessary as you want to add a class/styling to the document root or body, which is the default node.

Here is the current code for creating the Emphasize Titles plugin:

import { PluginActionClass } from 'classes/plugin/action/class';
import { PluginElementToggleable } from 'classes/plugin/element/toggleable';
import pluginStyles from 'styles/plugin-styles.scss';

export const pluginEmphasizeTitles = new PluginElementToggleable({
  title: 'Emphasize Titles',
  enabled: false,
  actions: [
    new PluginActionClass({
      name: 'emphasize-titles-action',
      klass: [pluginStyles.emphasizeTitles]

Almost everything is default, except it's explicitly disabled to start with (just to illustrate the ability). Note that we're passing a reference to the pluginStyles.emphasizeTitles class that we imported from the stylesheet, as seen below.

@import 'src/styles/variables';

.emphasizeTitles h1,
.emphasizeTitles h2,
.emphasizeTitles h3,
.emphasizeTitles h4,
.emphasizeTitles h5,
.emphasizeTitles h6 {
  outline: 2px solid rgba($default-highlight-color-tertiary, 0.5) !important;
  outline-offset: 1px !important;

This should make it easy for designers to alter the look and behavior of plugins that rely on class styling.

A PluginActionStyle action accepts a few different arguments to adjust its behavior as well, the primary of which is the IPluginActionStyleOptions interface which has a few important settings:

  • manipulationType: ValueManipulationType: As we saw before, this determines how the values affected by this Action are manipulated. They can be scaled as a percentage or absolute values, toggled on or off, or directly assigned values based on enabledValue and disabledValue properties.
  • baseValue: A good deal of the logic behind the PluginActionStyle is to find and handle existing property values for nodes it is manipulating. Part of this logic is to retain original values within the nodes by adding a data attribute that stores the original value. Thus, when the plugin is disabled we can revert back to the original value if necessary. The baseValue property is used to set an initial value of the searched property when a given node doesn't have a valid initial value of its own.
  • unitType: As before, the plugin will try to determine the unit type of the original value and retain/use it for its own adjustments. However, for properties where the original value may not contain a unit (such as letter-spacing) the unitType property can be specified to provide a fallback type.

A given element can have multiple child actions assigned to it, in the event that you wish to invoke multiple actions at once. For example, here we made a scaling plugin that adjusts the padding and margin of all div elements by 2px each step:

new PluginElementScalable({
  title: 'Adjust Div Margin/Padding',
  scalingIncrement: 2,
  actions: [
    new PluginActionStyle({
      style: {
        name: 'padding',
        manipulationType: ValueManipulationType.AbsoluteScaling,
        unitType: 'px'
      query: 'div'
    new PluginActionStyle({
      style: {
        name: 'margin',
        manipulationType: ValueManipulationType.AbsoluteScaling,
        unitType: 'px'
      query: 'div'

Adjusting State

The deepest level of configuration involves changing the underlying state of a plugin, which is necessary when you want to automatically update the UI when data changes. These are the main sections to adjust to alter state for a plugin:

  1. Change (or set) the getInstanceState property for the PluginElement instance. This method returns an object that contains only the relevant stateful information for the given element instance. For example, this is the getInstanceState method of the PluginElementScalable:
public getInstanceState(params?: {
  id?: string;
  enabled?: boolean;
  scalingFactor?: number;
}): any {
  return {
    id: params && ? :,
      params && params.enabled !== undefined ? params.enabled : this.enabled,
      params && params.scalingFactor
        ? params.scalingFactor
        : this.scalingFactor

The getInstanceState method serves two logical purposes. When called with no params it returns the default state of the element. However, when passed optional parameters it overrides those defaults with the passed values. This is useful in functional component useEffect callbacks to compare existing state to potentially updated state. Here we see an example from PluginElementStatic that determines whether to update the plugin (and thus its child PluginActions) based on whether the new state has a different enabled value.

useEffect(() => {
  const currentState = this.getInstanceState();
  const newState = this.getInstanceState({ enabled });

  if (enabled !== this.enabled) {
    this.enabled = enabled;

  // Update on change
  if (!isEqual(currentState, newState)) {
  1. Next, add a Reselect selector function somewhere outside of the custom plugin instantiation. For example, here's the enabledSelector creation method found in the state/index.tsx file.
export const makeElementEnabledSelector = () =>
    (state: any) => state.elements.elements,
    (_: any, id: any) => id,
    (elements: any, id: any) => find(elements, ['id', id]).enabled

The reselect library basically allows the use of useState-style hooks, but more efficiencly composes them to ensure proper memoization and efficiency. The way to look at the selection creator above is to know that the final argument passes to createSelector is always the combiner, which combines the return values of all previous argument (selectors) to create the final selector. So, the above selector starts by receiving the full state and returns the elements.elements collection. The second selector receives the state (which is ignored) plus an outside id argument. The combined selector takes the returned elements and id values and finds a single element and retrieves its enabled property.

  1. Now add a new reducer entry if the dispatch object you're passing has a new type that didn't exist prior. In this case we need to handle a dispatch type === 'count':
case 'count':
  return Object.assign({}, state, {
    elements: any) => {
      if ( === {
        return Object.assign({}, element, {
          count: !element.count
      return element;
  1. Finally, update the PluginElement.template property so it is aware of the changes to the state that you'd like to track. For example, here's a template that tracks a new stateful count property:
public template = (self: any) => {
  const dispatch = useDispatch();

  const selectCount = useMemo(makeElementCountSelector, []);
  const count = useSelector(state => selectCount(state,;

  useEffect(() => {
    const currentState = this.getInstanceState();
    const newState = this.getInstanceState({ count });

    if (count !== this.count) {
      this.count = count;

    // Update on change
    if (!isEqual(currentState, newState)) {

  const handleOnClick = useCallback(
    () =>
        type: 'count',
        payload: { id: }

  return (
      <h3>Counted {count} times</h3>
      <button type={'button'} onClick={handleOnClick}>
        Count it!

Widget Testing

Local Widget + Local Test Site

  1. Run yarn run dev.
  2. Open http://localhost:5000/basic/ to test local page.

Local Widget + Local API Server

  1. Run SaaS dashboard app locally.
  2. Run yarn run dev.
  3. Open http://localhost:5000/api/ to the tests/sites/api page, which includes script at localhost API address (default: http://localhost:84/api/widget).


  1. Visit a web page to be tested.
  2. Copy raw contents from build/index.js.
  3. Paste into Chrome Dev Tools.
  • Alternatively, create Bookmarklet that loads raw build/index.js content.
  • Alternatively, use local Git clone'd copy by adding build/index.js to Chrome Dev Tools > Filesystem > Workspace, then Ctrl + A to select and Ctrl + Shift + E to execute on current page.

Using Inline SVGs

  1. Add SVG file to src/assets/svg.
  2. Run npm run svg:optimize, which uses the svgo tool to minify.
  3. Reference the minified svg copy found in srv/assets/svg-minified:
.largeCursor * {
  cursor: url(src/assets/svg-minified/cursor-arrow.svg), default !important;

Known Issues

  • Building the first time after importing / referencing a new .scss style or file will fail, reporting the property doesn't exist in CssExports. This is due to the build order for TypeScript + SCSS imports. Just force a second build to resolve the issue.


An inline JavaScript accessibility widget.






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