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HTML 

              
                <h1>HTML 5.2 <code>dialog</code> element examples</h1>

<p>Works natively in Chrome and Opera at present [08/01/2018].<br>JavaScript ES6 applied to support non-supporting browsers. <a class=lnk href="https://caniuse.com/#feat=dialog" target=_blank title="[new window]">Can I use: dialog</a></p>

<p class=dialogSupported>This browser supports <code>dialog</code></p>
<p class=noDialogSupport>This browser doesn't natively support <code>dialog</code></p>


<h2>Full screen modal: <code>dialog.showModal()</code></h2>

<dialog id=dialog_1>
<!--   <div class=content> -->
    <h2>Dialog one title</h2>
    <p>Dialog copy content with a <a class=lnk href>contained link</a> to test keyboard focus.</p>
    <p><kbd>TAB</kbd> key focus is locked into the modal.<br><kbd>ESC</kbd> or click button to exit.</p>
    <button>Exit dialog</button>
<!--   </div> -->
</dialog>
<button id=btn-dialog_1>Button one <small>(follows dialog one)</small></button>


<button id=btn-dialog_2>Button two <small>(precedes dialog two)</small></button>
<dialog id=dialog_2>
  <h2>Dialog 2 title</h2>
  <p>Dialog copy content with a <a class=lnk href>contained link</a> to test keyboard focus.</p>
  <p><kbd>TAB</kbd> key focus is locked into the modal.<br><kbd>ESC</kbd> or click button to exit.</p>
  <button>Exit dialog</button>
</dialog>


<h2>Local modal: <code>dialog.show()</code></h2>

<p>Purposefully swapped <code>button</code> positions. Both precede <code>dialog</code> HTML.</p>


<!-- Swapped button positions -->
<button id=btn-dialog_4 data-dialog-type=show>Dialog four</button>
<button id=btn-dialog_3 data-dialog-type=show>Dialog three</button>


<dialog id=dialog_3>
  <h2>Dialog 3 title</h2>
  <p>Dialog copy content with a <a class=lnk href>contained link</a> to test keyboard focus.</p>
  <button>Exit dialog</button>
</dialog>


<dialog id=dialog_4>
  <h2>Dialog 4 title</h2>
  <p>Dialog copy content with a <a class=lnk href>contained link</a> to test keyboard focus.</p>
  <button>Exit dialog</button>
</dialog>

<p>Note how <code>z-index</code> layering remains in source code order.</p>
<p>Note when multiple <code>dialog</code>s are open reclicking the <code>button</code> doesn't bring the <code>dialog</code> to the front.</p>
<!-- <p><a class=lnk href>Empty link</a> to test if exiting modal returns user to activating button.</p> -->

<h2>Added via JS</h2>
<ul>
  <li>Return focus to the activating button upon close.</li>
  <li>Keyboard trap implemented for <code>showModal()</code> but not <code>show()</code>.</li>
</ul>

<h2>Working on</h2>
<ul>
  <li>Currently investigating what should occur, keyboard chain wise, when opened via <code>show()</code>.</li>
<li>Requires full testing with Voiceover and JAWS. None done so far.</li>
</ul>




[[[https://codepen.io/2kool2/pen/mKeeGM]]]
!

CSS 

              
                @media (min-width: 40em) {
  :root {
    /* Rough responsive fonts */
    font-size: calc(1vw + 1vh + .5vmin);
  }
}
body {
  font-family: sans-serif;
  line-height: 1.5;
  text-align: center;
  padding-bottom: 2rem;
}
body {
  color: hsl(269,19%,30%);
  background-color: hsla(32,100%,85%,.35);
  background-image: url("data:image/svg+xml;charset=utf8,%3Csvg width='100%25' xmlns='http://www.w3.org/2000/svg'%3E%3Cdefs%3E%3Cfilter id='a'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.4'/%3E%3C/filter%3E%3C/defs%3E%3C!-- %3Cpath filter='url(%23a)' opacity='.3' d='M0 0h1200v256H0z'/%3E--%3E%3Crect filter='url(%23a)' opacity='.3' width='100%25' height='100%25'/%3E%3C/svg%3E");
}
h1,h2 {
  font-weight: 100;
  margin-top: 2rem;
  margin-bottom: 1rem;
}
p {
  max-width: 40em;
  margin: 1rem auto;
}
.lnk {
  color: hsl(211, 100%, 40%); /* Brightest WCAG against #DAE5F2 */
  text-decoration-skip: ink;
  text-decoration-color: hsla(211, 100%, 40%, .25);
  outline: 0 solid #fff;
  transition: background-color .3s;
}
.lnk:hover,
.lnk:focus {
  color: hsl(211, 100%, 46%); /* Brightest WCAG against #fff */
  background-color: #fff;
  text-decoration-color: hsla(211, 100%, 46%, 1);
  outline: .25rem solid #fff;
  transition: outline .3s;
}
kbd,
code {
  font-size: inherit;
  font-weight: 100;
  font-family: monospace, monospace;
  text-shadow: .03125em .03125em #fff;
  background-color: hsla(32,100%,100%,.35);
/*   outline: .25em solid hsla(32,100%,100%,.35); */
  padding: 0 .25em;
}
ul {
  max-width: 30em;
  text-align: left;
  margin: 1rem auto;
}

button {
  margin: 1rem;
  font-size: 1.25rem;
  padding: 1rem 1.5rem;
  color: inherit;
  background-color: hsla(32,100%,100%,.75);
  border: 1px solid #fff;
  box-shadow: 0 2px 4px rgba(0,0,0,.5);
  transition: all .3s ease-out;
  cursor: pointer;
}
button:hover {
  color: #000;
  background-color: hsla(32,100%,100%,1);
  box-shadow: 0 4px 8px rgba(0,0,0,.25);
}


dialog,
dialog[close],
dialog[aria-hidden="true"] {
/*   display: none; */
  visibility: hidden;
  opacity: 0;
  transition: 
    display 0s linear 2s,
    visibility 0s linear 2s,
    opacity 1s ease-out 0s;
}
dialog[open],
dialog[aria-hidden="false"]{
  display: block;
  visibility: visible;
  opacity: 1;
  color: inherit;
  background-color: hsla(32,50%,95%,1);
  transition: 
    display 0s linear 0s, 
    visibility 0s linear 0s, 
    opacity 1s ease-out 0s;
}
dialog::backdrop{
  background-color: hsla(32,50%,10%,.7);
}

/* Making a dialog work in unsupported browsers */
dialog {
  --spacing: 1rem;
  box-sizing: border-box;
  border: 2px solid #000;
  padding: var(--spacing);
}
dialog[aria-hidden][data-dialog-type="showModal"] {
  position: fixed;
  z-index: 20;
  top: 50%;
  left: 50%;
  transform: translate3d(-50%, -50%, 0);
}
dialog[aria-hidden][data-dialog-type="show"] {
  position: absolute;
  left: 50%;
  transform: translate3d(-50%, 0, 0);
}
.-js-dialogBg {
  position: fixed;
  z-index: 10;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background-color: hsla(32,50%,10%,.7);
}
.-js-dialogBg:hover {
  /* Stolen from trickle.js. SVGs will not work here */
  cursor: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAAAXNSR0IArs4c6QAAANpJREFUOBGNkz0KAjEQhYPYWXgCKws7LcXWyt7WG4i9jegBvIJ4AvEyXsRCsBDiN0sGkiE/O/A2O9n3viS7rPPeb9ETrVzPwrtHDzR1XF5I6oPWLQaeq5hDXQRw0I6xCuF5HH7Tz7oFuTkhrSyEhza8THaLoQhphpWUg/QOFyA/AFpy5nTbGrIjxvg4AiiGBzYc+rGZH9KPzFy+ZbX4bX9l+VDZr5NQMMbhbtvMxccpQ3JhpTchtXATQviItIpvW0CY7HHm8c9UDRd2chbABt3RQk2tEe8O3dDkD4JQ4iOR7BMpAAAAAElFTkSuQmCC"), pointer;
}
.dialogSupported,
.noDialogSupport {
  font-weight: bold;
}
.dialogSupported,
.supportsDialog .noDialogSupport {
  display: none;
}
.supportsDialog .dialogSupported {
  display: inline;
}
!

JS 

              
                
// Not required but useful
if (typeof HTMLDialogElement === "function") {
  document.documentElement.classList.add("supportsDialog");
}



(function() {

  "use strict";

  const bgClass = "-js-dialogBg";
  const dataAttr = "data-dialog-type";

  const _removeDialogBackground = () => {
    const bg = document.querySelector("." + bgClass);
    if (bg) {
      document.body.removeChild(bg);
    }
  };

  const _dialogClose = (dialog) => {
    if (dialog.close) {
      dialog.close();
    } else {
      dialog.setAttribute("aria-hidden", "true");
      _removeDialogBackground();
    }
    dialog.btnOpen.focus();
  };

  const _appendDialogBackground = (dialog) => {
    const bg = document.createElement("div");
    const hasBg = document.querySelector("." + bgClass);
    if (!hasBg) {
      bg.addEventListener("click", function() {
        _dialogClose(dialog);
      });
      bg.classList.add(bgClass);
      document.body.appendChild(bg);
    }
  };

  const _keydown_modal = (e) => {

    const target = e.target;
    const parentDialog = target.closest("dialog");

    if (!parentDialog) {
      return false;
    }

    // console.log(target.tagName, parentDialog.tagName);

    // ESC key on anything actionable
    if (e.which === 27) {
      _dialogClose(parentDialog);
    }

    // tab key and shift on the first element
    if (e.which === 9 && e.shiftKey && target === parentDialog.firstElementChild) {
      e.preventDefault();
      parentDialog.lastElementChild.focus();
    }

    // tab key and not shift on the last element.
    if (e.which === 9 && !e.shiftKey && target === parentDialog.lastElementChild) {
      e.preventDefault();
      parentDialog.firstElementChild.focus();
    }

  };

  const _showModal = (dialog) => {
    if (dialog.showModal) {
      dialog.showModal();
    } else {
      _appendDialogBackground(dialog);
      dialog.setAttribute("aria-hidden", "false");
      dialog.setAttribute(dataAttr, "showModal");
    }
    dialog.addEventListener("keydown", _keydown_modal, false);
  };

  const _show = (dialog) => {
    if (dialog.show) {
      dialog.show();
    } else {
      dialog.setAttribute("aria-hidden", "false");
      dialog.setAttribute(dataAttr, "show");
    }
  };

  const _dialogOpen = (dialog) => {
    const isShowModal = dialog.btnOpen.getAttribute(dataAttr) !== "show";
    if (isShowModal) {
      _showModal(dialog);
    } else {
      _show(dialog);
    }
    dialog.firstElementChild.focus();
  };


  const dialogs = document.querySelectorAll("dialog");
  for (const dialog of dialogs) {

    // Close button
    const btnClose = dialog.querySelector("button");
    if (btnClose) {
      btnClose.addEventListener("click", () => _dialogClose(dialog));
    }

    // Close when clicking on dialog::backdrop
    // Method and code from: https://codepen.io/keithjgrant/pen/eyMMVL
    // - Only works when a container inside completely fills the dialog.
    // - first-child focus would require adjustment to suit.
    // dialog.addEventListener('click', (event) => {
    //   console.log(event.target);
    //   if (event.target === dialog) {
    //     _dialogClose(dialog);
    //   }
    // }, false);

    // Open Button
    const btnOpen = document.getElementById("btn-" + dialog.id);
    if (btnOpen) {
      btnOpen.addEventListener("click", () => {
        dialog.btnOpen = btnOpen;
        _dialogOpen(dialog);
      });
    }

    // focussable first child
    const firstElement = dialog.firstElementChild;
    if (firstElement) {
      firstElement.setAttribute("tabindex", "0");
    }

  }

})();
!
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