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dialog-polyfill.js is a polyfill for <dialog> and <form method="dialog">. Check out some demos!

<dialog> is an element for a popup box in a web page, including a modal option which will make the rest of the page inert during use. This could be useful to block a user's interaction until they give you a response, or to confirm an action. See the HTML spec.

Usage

Installation

You may optionally install via NPM or Bower-

$ npm install dialog-polyfill
$ bower install dialog-polyfill

Supports

This polyfill works on modern versions of all major browsers. It also supports IE9 and above.

Steps

  1. Include the CSS in the <head> of your document, and the Javascript anywhere before referencing dialogPolyfill.
  2. Create your dialog elements within the document. See limitations for more details.
  3. Register the elements using dialogPolyfill.registerDialog(), passing it one node at a time. This polyfill won't replace native support.
  4. Use your <dialog> elements!

Example

<head>
  <link rel="stylesheet" type="text/css" href="dialog-polyfill.css" />
</head>
<body>
  <dialog>
    I'm a dialog!
    <form method="dialog">
      <input type="submit" value="Close" />
    </form>
  </dialog>
  <script src="dialog-polyfill.js"></script>
  <script>
    var dialog = document.querySelector('dialog');
    dialogPolyfill.registerDialog(dialog);
    // Now dialog acts like a native <dialog>.
    dialog.showModal();
  </script>
</body>

::backdrop

In native <dialog>, the backdrop is a pseudo-element. When using the polyfill, the backdrop will be an adjacent element:

dialog::backdrop { /* native */
  background-color: green;
}
dialog + .backdrop { /* polyfill */
  background-color: green;
}

Limitations

In the polyfill, modal dialogs have limitations-

  • They should not be contained by parents that create a stacking context, see below
  • The browser's chrome may not always be accessible via the tab key
  • Changes to the CSS top/bottom values while open aren't retained

Stacking Context

The major limitation of the polyfill is that dialogs should not have parents that create a stacking context. The easiest way to solve this is to move your <dialog> element to be a child of <body>.

If this isn't possible you may still be able to use the dialog. However, you may want to resolve it for two major reasons-

  1. The polyfill can't guarantee that the dialog will be the top-most element of your page
  2. The dialog may be positioned incorrectly as they are positioned as part of the page layout where they are opened (defined by spec), and not at a fixed position in the user's browser.

To position a dialog in the center (regardless of user scroll position or stacking context), you can specify the following CSS-

dialog {
  position: fixed;
  top: 50%;
  transform: translate(0, -50%);
}

Extensions

Focus

The WAI-ARIA doc suggests returning focus to the previously focused element after a modal dialog is closed. However, this is not part of the dialog spec itself. See this snippet to add this, even to the native dialog.