A vanilla JavaScript, accessible modal dialog script, written in ES5.

See the live demo and test pages.

Please read Having an open dialog, which provides information on the support for the native <dialog> element. As browser support (particularly Safari 15.4 and up adoption) increases, the need for custom dialogs should significantly decrease, rendering custom solutions such as this one here unnecessary.

NOTE: this script is not under active development. I would recommend either using the native <dialog> element, or you should check out a11y-dialog for a script that is being actively maintained and delivers a good modal dialog experience.

You can get this package on npm:

$ npm i aria-modal-dialog

Clone it:

$ git clone https://github.com/scottaohara/accessible_modal_window.git

Or download a zip of the repository.

The CSS for this component is included in assets/css/. The classes are added to the base markup when the script/page loads. The base CSS has only the most necessary styling to visually convey it as a modal dialog. You will need to modify the CSS to integrate the dialog into your project's visual aesthetic.

Include the a11y.modal.js file at the bottom of your document, or concatenated into your primary .js file, as part of your build process.

Ideally modal dialogs are activated by a purposeful user interaction with a button, or an element that has been modified to have the semantics and keyboard functionality of a button. While this script does allow dialogs to be activated by other means, a dialog opening without a purposeful action can be a confusing and frustrating user experience to many.

The baseline for a button to open a modal dialog should consist of the following:

<button type="button"
  class="_your_class(es)_here_"
  data-modal-open="IDREF_of_modal_to_open"
  disabled>
  Launch My Modal
</button>
<!--
  Swap out disabled with the hidden attribute if you want the trigger to be 
  completely hidden if JavaScript is unavailable for some reason.  

  The hidden attribute and/or the disabled attribute will be removed 
  during the script's setup function.
-->

The data-modal-open attribute is used to point to the specific modal dialog the button should activate. Adding a disabled attribute helps ensure that if JavaScript is blocked, or fails, users will be presented with a button that correctly conveys current functionality.

If JavaScript is unavailable, and the contents of a modal dialog would still make sense as part of the document, then an <a> element may be used as the dialog trigger, and progressively enhanced to be a button. This would then allow the <a> to act as an in-page link to the would-be dialog's contents.

<a href="#unique_ID_2"
  class="_your_class(es)_here_" 
  data-modal-open>
  Launch My Modal
</a>

The href attribute of a link may act as the identifier for the target dialog, if the data-modal-open attribute value is empty. However, if you would like this link to go to another location, if JavaScript were disabled, then set the href to the appropriate URL, and set the data-modal-open to the IDREF of the dialog within the document. Note, the href is removed from the <a> when the script runs, and a tabindex=0 is added, as "buttons" shouldn't allow for right click to open in a new window.

The minimum markup for a modal dialog would be the following:

<div id="unique_ID_to_match_data-modal-open" data-modal>
  <h1>
    A descriptive title for the dialog
  </h1>
  <div>
    <!-- primary content of the dialog here -->
  </div>
</div>

If you need to support NVDA prior to 2017.4, then consider the following minimum markup pattern, which will add a role="document" to the div that wraps the contents of the modal dialog. This will correctly allow users to navigate the contents of a dialog with NVDA's virtual cursor, and not automatically enter users into forms/application mode:

Update: This pattern should also be considered for macOS VoiceOver users, as without a role=document wrapping all the contents within a role=dialog, VoiceOver's quick nav may not be able to access all elements. Without quick nav on, VoiceOver should have no issues accessing content of a role=dialog.

<div id="unique_ID_to_match_data-modal-open" data-modal>
  <div data-modal-document>
    <h1>
      A descriptive title for the dialog
    </h1>
    <div>
      <!-- primary content of the dialog here -->
    </div>
  </div>
</div>

This script does not presently use the aria-haspopup="dialog" on a dialog's trigger(s). Nor does it use aria-modal on the element with role="dialog". The code to add these attributes are currently in the dialog script, but commented out until they receive more robust support (see Screen Reader quirks).

Update August 15, 2018: Testing with Safari Technology Preview (Release 63 (Safari 12.1, WebKit 13607.1.2.1)) on macOS 10.13.6, aria-modal="true" will begin to work properly with VoiceOver. This is great news for the future, but until a good percentage of people update from Safari 11.x to 12+, aria-modal should continued to be used with caution.

For this script to provide peak accessibility, it must also utilize the inert polyfill from Google. While the dialogs have a function to keep focus within the dialog, looping through any focusable elements within itself, the inert polyfill will help prevent a user from accessing the browser's chrome (e.g. the address bar) and then being able to navigate back into the obscured document. The dialog script doubles down on the elements with inert="true" and also add an aria-hidden="true" as well. This ensures that not only can users not access elements within the obscured document by keyboard navigation, but that these elements will not be revealed in screen reader listings of elements within a document (e.g. listings of landmarks/regions, headings or form controls with NVDA and JAWS, or be revealed in VoiceOver's rotor menus.)

The following attributes are used to setup instances of the dialog triggers (buttons), the dialog container, and any necessary child elements of the dialogs.

• data-modal-open: If used on a button or element with role=button, this attribute must contain the id of the dialog it is to activate. If used on an a element with an href pointing to the dialog it is to activate, then this attribute can be set to the empty string.
• hidden: Use this attribute to hide a trigger in the event that JavaScript is unavailable and it wouldn't make sense for the trigger to be available to users.
• disabled: Set to a trigger to disable it in the event that JavaScript is unavailable and the trigger would perform no function.
• data-modal-auto: Indicates that the trigger's associated modal dialog should activate on page load.
• data-modal-auto-persist: Indicates that the trigger's associated modal dialog should continue to activate on page reload. Without this attribute, the associated modal dialog will only auto activate once.

• data-modal: The primary hook for indicating the element is meant to be transformed into a modal dialog. Leaving the attribute's value empty will result in a standard role="dialog". Setting the value to be "alert" will indicate that the script should add role="alertdialog" to the element.
• data-modal-class: Setting a value to this attribute will add the value as a class name to the dialog when JavaScript is enabled. Useful if you want to progressively enhance the markup from static content to a modal dialog, but don't want it to visually look like a dialog without JavaScript.
• data-modal-hide-heading: This attribute will set a class of at-only to the first heading of the modal dialog.
• data-modal-close: Adding a value to this attribute will change the auto generated close button from an "icon" button to an inline button with a visible label of the value.
• data-modal-close-class: The value set to this attribute will be become a class name added to generated close button.
• data-modal-focus-close: This attribute serves as a hook to autofocus the generated close button when the dialog is opened.
• data-modal-manual-close: If you want full control over where your close button goes, adding this attribute to the dialog container will stop the generation of a close button. It's up to you to hard code the close button yourself.
• data-modal-auto: Indicates this modal dialog should activate on page load.
• data-modal-auto-persist: Indicates that this modal dialog should continue to activate on page reload. Without this attribute, the modal dialog will only auto activate once.
• hidden: All dialogs that are not meant to be visible if JavaScript or CSS are disabled should have this attribute.

• autofocus: If a dialog has this attribute on a child element, move focus to this element instead of the dialog container.
• data-autofocus: Since it is invalid to have multiple autofocus attributes in a single document, but there may be multiple dialog instances, use this attribute to simulate an automatic focus with JavaScript.
• data-modal-description: This attribute will be used to auto-generate a unique ID, and become the pointer for the generated aria-describedby that is added to the dialog container.
• data-modal-close-btn: Add this attribute to button elements within the dialog that should be allowed to close the dialog.

Things of note for why certain decisions were made, and how different screen reader and browser combos have their own inconsistencies in announcing modal dialogs.

• Do not set dialogs to display: none by default.
  There is an issue with iOS Safari + VoiceOver where if an element is set to display: none; by default, even when set to display: block; VO will not move focus to the element, even if focus is programmatically set. To get around this, the CSS for these dialogs use visibility: hidden; for the inactive state, and visibility: visible; for showing the dialog.

  As visibility: hidden does not remove an element from the document's flow, it's important that position: absolute/fixed is set to the dialog, regardless of whether it's active or not.

• The first element of a modal dialog should be its heading (which provides its accessible name). This requirement is to compensate for Internet Explorer 11 + JAWS specifically, when the dialog element is focused by default. With this pairing, setting focus to the dialog element itself will announce the accessible name of the dialog, the dialog role, and then JAWS will announce re-announce the accessible name of the dialog and the role of the first child element of the dialog. For instance, if the dialog's heading provides the accessible name for the dialog, then JAWS + IE11 will announce "accessible name, dialog. accessible name, heading level #". However, if the first child is another element that does not match the accessible name of the dialog, such as a button with text "close", it will be announced as: "accessible name, dialog. accessible name, button"

• If using macOS VoiceOver's (tested with version 8 and 9) quick navigation the contents of modal dialogs may be inaccessible if the dialog element has an accessible name set by aria-label or aria-labelledby. To mitigate this, either do not set an accessible name to the modal dialog, or wrap the contents of the modal dialog within a role="document".

• Note that NVDA will not announce the dialog role when focus is set to the dialog element itself. For instance, in NVDA + IE11, it will simply announce the accessible name of the dialog, and nothing more. In more standard browser pairings like Firefox or Chrome, the accessible name of the dialog will be announced, and then the contents of the dialog will begin to be announced, without ever mentioning the dialog role.

Articles I've written about modal dialog accessibility.

• Having an open dialog (2019 / updated 2022)
• The state of modal dialog accessibility (2018)
• Accessible Modals: Revisited (version 2 release article) (2016)
• Making modal windows better for everyone - Smashing Magazine (2014)

This script was written by Scott O'Hara: Website, Twitter.

It has an MIT license.

Use it, modify it, contribute to it to help make your project more accessible :)