Add Focus To Pop Up / Modal On Click For Tabbing / Accessibility - JavaScript

There are a few things to consider when making your modal dialog accessible that go beyond just setting focus to your modal or retricting tab order within the modal. You also have to consider that screen readers can still perceive the underlying page elements if they're not hidden from the screen reader using aria-hidden="true", and then you also need to un-hide those elements when the modal is closed and the underlying page is restored.

So, to summarise, what you need to do is:

1. Set focus to the first focusable element inside the modal when it appears.
2. Ensure that the underlying page elements are hidden from the screen reader.
3. Ensure that tab order is restricted inside the modal.
4. Ensure that expected keyboard behaviour is implemented, e.g., pressing Escape will close or dismiss the modal dialog.
5. Ensure that the underlying page elements are restored when the modal is closed.
6. Ensure that the element that previously had focus prior to the modal dialog being opened has focus restored to it.

You also need to ensure that your modal dialog has the ARIA role="dialog" attribute so that screen readers will announce that focus has moved to a dialog, and ideally you should use the aria-labelledby and/or aria-describedby attributes to provide an accessible name and/or description to your modal.

That's quite a list, but it's what is generally recommended for accessible modal dialogs. See the WAI-ARIA Modal Dialog Example.

I've written a solution for your modal, partially based on Hidde de Vries's original code for restricting tab order inside a modal dialog.

The trapFocusInModal function makes a node list of all focusable elements and adds a key listener for Tab and Shift+Tab keys to ensure focus doesn't move beyond the focusable elements in the modal. The key listener also binds to the Escape key to close the modal.

The openModal function displays the modal dialog, hides the underlying page elements, places a class name on the element that last held focus before the modal was opened and sets focus to the first focusable element in the modal.

The closeModal function closes the modal, un-hides the underlying page, and restores focus the element that last held focus before the modal was opened.

The domIsReady function waits for the DOM to be ready and then binds the Enter key and mouse click events to the openModal and closeModal functions.

Codepen: https://codepen.io/gnchapman/pen/JjMQyoP

const KEYCODE_TAB = 9;
const KEYCODE_ESCAPE = 27;
const KEYCODE_ENTER = 13;

// Function to open modal if closed
openModal = function (el) {

    // Find the modal, check that it's currently hidden
    var modal = document.getElementById("modal");
    if (modal.style.display === "") {
        
        // Place class on element that triggered event
        // so we know where to restore focus when the modal is closed
        el.classList.add("last-focus");

        // Hide the background page with ARIA
        var all = document.querySelectorAll("button#click-me,input");
        for (var i = 0; i < all.length; i++) {
            all[i].setAttribute("aria-hidden", "true");
        }
        
        // Add the classes and attributes to make the modal visible
        modal.style.display = "flex";
        modal.setAttribute("aria-modal", "true");
        modal.querySelector("button").focus();
    }
};

// Function to close modal if open
closeModal = function () {

    // Find the modal, check that it's not hidden
    var modal = document.getElementById("modal");
    if (modal.style.display === "flex") {

        modal.style.display = "";
        modal.setAttribute("aria-modal", "false")

        // Restore the background page by removing ARIA
        var all = document.querySelectorAll("button#click-me,input");
        for (var i = 0; i < all.length; i++) {
            all[i].removeAttribute("aria-hidden");
        }
        
        // Restore focus to the last element that had it
        if (document.querySelector(".last-focus")) {
            var target = document.querySelector(".last-focus");
            target.classList.remove("last-focus");
            target.focus();
        }
    }
};

// Function to trap focus inside the modal dialog
// Credit to Hidde de Vries for providing the original code on his website:
// https://hidde.blog/using-javascript-to-trap-focus-in-an-element/
trapFocusInModal = function (el) {

    // Gather all focusable elements in a list
    var query = "a[href]:not([disabled]), button:not([disabled]), textarea:not([disabled]), input[type='email']:not([disabled]), input[type='text']:not([disabled]), input[type='radio']:not([disabled]), input[type='checkbox']:not([disabled]), select:not([disabled]), [tabindex='0']"
    var focusableEls = el.querySelectorAll(query);
    var firstFocusableEl = focusableEls[0];
    var lastFocusableEl = focusableEls[focusableEls.length - 1];

    // Add the key listener to the modal container to listen for Tab, Enter and Escape
    el.addEventListener('keydown', function(e) {
        var isTabPressed = (e.key === "Tab" || e.keyCode === KEYCODE_TAB);
        var isEscPressed = (e.key === "Escape" || e.keyCode === KEYCODE_ESCAPE);
  
        // Define behaviour for Tab or Shift+Tab
        if (isTabPressed) {
            // Shift+Tab
            if (e.shiftKey) {
                if (document.activeElement === firstFocusableEl) {
                    lastFocusableEl.focus();
                    e.preventDefault();
                }
            }
            
            // Tab
            else {
                if (document.activeElement === lastFocusableEl) {
                    firstFocusableEl.focus();
                    e.preventDefault();
                }
            }
        }
        
        // Define behaviour for Escape
        if (isEscPressed) {
            el.querySelector("button.close").click();
        }
    });
};

// Cross-browser 'DOM is ready' function
// https://www.competa.com/blog/cross-browser-document-ready-with-vanilla-javascript/
var domIsReady = (function(domIsReady) {

    var isBrowserIeOrNot = function() {
        return (!document.attachEvent || typeof document.attachEvent === "undefined" ? 'not-ie' : 'ie');
    }

    domIsReady = function(callback) {
        if(callback && typeof callback === 'function'){
            if(isBrowserIeOrNot() !== 'ie') {
                document.addEventListener("DOMContentLoaded", function() {
                    return callback();
                });
            } else {
                document.attachEvent("onreadystatechange", function() {
                    if(document.readyState === "complete") {
                        return callback();
                    }
                });
            }
        } else {
            console.error('The callback is not a function!');
        }
    }

    return domIsReady;
})(domIsReady || {});


(function(document, window, domIsReady, undefined) {

    // Check if DOM is ready
    domIsReady(function() {

        // Write something to the console
        console.log("DOM ready...");
        
        // Attach event listener on button elements to open modal
        if (document.getElementById("click-me")) {
                
            // Add click listener
            document.getElementById("click-me").addEventListener("click", function(event) {
                // If the clicked element doesn't have the right selector, bail
                if (!event.target.matches('#click-me')) return;
                event.preventDefault();
                // Run the openModal() function
                openModal(event.target);
            }, false);

            // Add key listener
            document.getElementById("click-me").addEventListener('keydown', function(event) {
                if (event.code === "Enter" || event.keyCode === KEYCODE_ENTER) {
                    // If the clicked element doesn't have the right selector, bail
                    if (!event.target.matches('#click-me')) return;
                    event.preventDefault();
                    // Run the openModal() function
                    openModal(event.target);
                }
            });
        }

        // Attach event listener on button elements to close modal
        if (document.querySelector("button.close")) {
                
            // Add click listener
            document.querySelector("button.close").addEventListener("click", function(event) {
                // If the clicked element doesn't have the right selector, bail
                if (!event.target.matches('button.close')) return;
                event.preventDefault();
                // Run the closeModal() function
                closeModal(event.target);
            }, false);

            // Add key listener
            document.querySelector("button.close").addEventListener('keydown', function(event) {
                if (event.code === "Enter" || event.keyCode === KEYCODE_ENTER) {
                    // If the clicked element doesn't have the right selector, bail
                    if (!event.target.matches('button.close')) return;
                    event.preventDefault();
                    // Run the closeModal() function
                    closeModal(event.target);
                }
            });
        }

        // Trap tab order within modal
        if (document.getElementById("modal")) {
            var modal = document.getElementById("modal");
            trapFocusInModal(modal);
        }
        
   });
})(document, window, domIsReady);

<button id="click-me">Click Me</button>
<form action="">
    <input placeholder="An Input" type="text"> <input placeholder="An Input" type="text"> <input placeholder="An Input" type="text"> <input placeholder="An Input" type="text">
</form>
<div class="modal" id="modal" role="dialog">
    <button class="close">Close x</button> <button>More Buttons</button> <button>More Buttons</button>
</div>

body {
  margin: 0;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}

input, button {
  margin: 1rem;
  padding: .5rem;
}
.click-me {
  display: block;
}

.modal {
  display: none;
  flex-direction: column;
  width: 100%;
  height: 100%;   
  justify-content: center;
  align-items: center;
  background: grey;
  position: absolute;
}

form {
  display: flex;
}

You have to add focus to the pop-up right after this appears, when you do it simultaneously with closeButton.focus() only it won't work that's why I'm using setTimeout(() => closeButton.focus(), 1), this will added it focus after a 1 millisecond.

At first, focus on a button isn't visible, it become visible when arrow keys are pressed, so I make it visible styling it:

      .close:focus {
        border: 2px solid black;
        border-radius: 5px;
      }

The whole code:

      let clickMe = document.querySelector("#click-me"),
        modal = document.querySelector(".modal"),
        closeButton = document.querySelector(".close");

      clickMe.addEventListener("click", () => {
        setTimeout(() => closeButton.focus(), 1);
        modal.style.display = "flex";
      });

      closeButton.addEventListener("click", () => {
        modal.style.display = "none";
      });

      body {
        margin: 0;
        height: 100vh;
        display: flex;
        justify-content: center;
        align-items: center;
        flex-direction: column;
      }

      input,
      button {
        margin: 1rem;
        padding: 0.5rem;
      }
      .click-me {
        display: block;
      }

      .modal {
        display: none;
        flex-direction: column;
        width: 100%;
        height: 100%;
        justify-content: center;
        align-items: center;
        background: gray;
        position: absolute;
      }

      form {
        display: flex;
      }
      .close:focus {
        border: 2px solid black;
        border-radius: 5px;
      }

    <button id="click-me">Click Me</button>
    <form action="">
      <input type="text" placeholder="An Input" />
      <input type="text" placeholder="An Input" />
      <input type="text" placeholder="An Input" />
      <input type="text" placeholder="An Input" />
    </form>

    <div class="modal">
      <button class="close">Close x</button>
      <button>More Buttons</button>
      <button>More Buttons</button>
    </div>

UPDATE: The focus jumps only within the modal:

     let clickMe = document.querySelector("#click-me"),
        modal = document.querySelector(".modal"),
        closeButton = document.querySelector(".close");
      lastButton = document.querySelector(".lastButton");
      clickMe.addEventListener("click", () => {
        setTimeout(() => closeButton.focus(), 1);
        modal.style.display = "flex";
      });

      closeButton.addEventListener("click", () => {
        modal.style.display = "none";
      });

      modal.addEventListener("keydown", function (event) {
        var code = event.keyCode || event.which;
        if (code === 9) {
          if (lastButton == document.activeElement) {
            event.preventDefault();
            closeButton.focus();
          }
        }
      });

body {
        margin: 0;
        height: 100vh;
        display: flex;
        justify-content: center;
        align-items: center;
        flex-direction: column;
      }

      input,
      button {
        margin: 1rem;
        padding: 0.5rem;
      }
      .click-me {
        display: block;
      }

      .modal {
        display: none;
        flex-direction: column;
        width: 100%;
        height: 100%;
        justify-content: center;
        align-items: center;
        background: gray;
        position: absolute;
      }

      form {
        display: flex;
      }
      .close:focus {
        border: 2px solid black;
        border-radius: 5px;
      }

<button id="click-me">Click Me</button>
    <form action="">
      <input type="text" placeholder="An Input" />
      <input type="text" placeholder="An Input" />
      <input type="text" placeholder="An Input" />
      <input type="text" placeholder="An Input" />
    </form>

    <div class="modal">
      <button class="close">Close x</button>
      <button>More Buttons</button>
      <button class="lastButton">More Buttons</button>
    </div>

Moving focus into the modal

To put focus into the modal, you have to put focus onto a focusable element within the modal, which is why doing modal.focus(); did not result in the focus moving into the modal like you wished since modal itself isn't a focusable element. Instead, you would want to do something such as $(modal).find("button").first().focus(); instead.

User2495207 showed you another way to do this, but setTimeout is prone to bugs and unnecessary. We also ideally don't want to dictate that it should focus on a specific button, just whichever is the first button found in the tab order.

This only solves the problem of moving the focus into the modal initially, however. It does not trap the focus within the modal, so when you tab past the last button, it will move focus to elements behind the modal.

Trapping focus in the modal

The idea here is that you want to check if the next focusable element is within the modal or not, and if not then that means you were on the last element in the modal and need to wrap focus to the first element in the modal. You should also reverse this logic where if the first button is focused and someone presses shift+tab it'll wrap to the last element in the modal, but I am just going to demonstrate the first scenario:

let clickMe = document.querySelector('#click-me'),
    modal = document.querySelector('.modal'),
    closeButton = document.querySelector('.close')

clickMe.addEventListener('click', () =>{
  modal.style.display = 'flex';
  $(modal).find("button").first().focus();

  trapFocus(modal);
});

function trapFocus(modal) {
  $(modal).find("button").last().on('blur', (e) => {
    // found something outside the modal
    if (!$(modal).find($(e.relatedTarget)).length > 0) {
      e.preventDefault();
      $(modal).find("button").first().focus();
    }
  });
}

closeButton.addEventListener('click', () =>{
  modal.style.display = 'none';
});

RelatedTarget is a great tool that allows you to intercept focus events to determine where the focus is going. So in the code above, we are checking if the element that is about to be focused, aka relatedTarget, is within the modal, if it is not, then we force focus where we want it to go.

One last note about Accessibility

You also want to be sure to make the modal close on keydown of Escape. On this note, e.keyCode is deprecated, and we should all be using e.key.

If you need to support IE, first of all, I am sorry. Second of all, it requires e.keyCode to function properly so it needs to be used in conjunction with your e.key check, such as e.key === "Escape" && e.keyCode === "27". I do recommend, however, maybe just making a function that accepts the event as a parameter, and keeping these checks within that function so when IE eventually makes support for e.key then you can cleanup your code all in one spot.

I trying easiest solution present to you.

So my solution is this:

1.finding all focus-able elements in the modal.

let modelElement = document.getElementById("modal");
let focusableElements = modelElement.querySelectorAll('a[href], area[href], input:not([disabled]), select:not([disabled]), textarea:not([disabled]), button:not([disabled]), iframe, object, embed, *[tabindex], *[contenteditable]');

2.listen to change focus on the web page.

3.In the focus listener method, it is checked that if modal is open and focused element not exist in the focus-able elements list, first element of focus-able elements list must be focus.

document.addEventListener('focus', (event) => { 
    if(modal.style.display == 'flex' && !Array.from(focusableElements).includes(event.target))
        Array.from(focusableElements)[0].focus();
}, true);

Final code:

let clickMe = document.querySelector('#click-me'),
modal = document.querySelector('.modal'),
closeButton = document.querySelector('.close')
console.log(clickMe)


clickMe.addEventListener('click', () =>{
  modal.style.display = 'flex';
  // modal.focus();
})

closeButton.addEventListener('click', () =>{
  modal.style.display = 'none';
})

let modelElement = document.getElementById("modal");
let focusableElements = modelElement.querySelectorAll('a[href], area[href], input:not([disabled]), select:not([disabled]), textarea:not([disabled]), button:not([disabled]), iframe, object, embed, *[tabindex], *[contenteditable]');

document.addEventListener('focus', (event) => { 
  if(modal.style.display == 'flex' && !Array.from(focusableElements).includes(event.target))
  Array.from(focusableElements)[0].focus();
}, true);

body {
  margin: 0;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}

input, button {
  margin: 1rem;
  padding: .5rem;
}
.click-me {
  display: block;
}

.modal {
  display: none;
  flex-direction: column;
  width: 100%;
  height: 100%;   
  justify-content: center;
  align-items: center;
  background: grey;
  position: absolute;
}

form {
  display: flex;
}

<button id="click-me">Click Me</button>
<form action="">
  <input type="text" placeholder="An Input">
  <input type="text" placeholder="An Input">
  <input type="text" placeholder="An Input">
  <input type="text" placeholder="An Input">
</form>

<div id="modal" class="modal">
  <button class="close">Close x</button>
  <button>More Buttons</button>
  <button>More Buttons</button>
</div>