@wavemaker/focus-trap
v1.0.1
Published
Trap focus within a DOM node.
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focus-trap
Trap focus within a DOM node.
There may come a time when you find it important to trap focus within a DOM node — so that when a user hits Tab
or Shift+Tab
or clicks around, she can't escape a certain cycle of focusable elements.
You will definitely face this challenge when you are trying to build accessible modals.
This module is a little, modular vanilla JS solution to that problem.
Use it in your higher-level components. For example, if you are using React check out focus-trap-react, a light wrapper around this library. If you are not a React user, consider creating light wrappers in your framework-of-choice.
What it does
When a focus trap is activated, this is what should happen:
- Some element within the focus trap receives focus. By default, this will be the first element in the focus trap's tab order (as determined by tabbable). Alternately, you can specify an element that should receive this initial focus.
- The
Tab
andShift+Tab
keys will cycle through the focus trap's tabbable elements but will not leave the focus trap. - Clicks within the focus trap behave normally; but clicks outside the focus trap are blocked.
- The
Escape
key will deactivate the focus trap.
When the focus trap is deactivated, this is what should happen:
- Focus is passed to whichever element had focus when the trap was activated (e.g. the button that opened the modal or menu).
- Tabbing and clicking behave normally everywhere.
For more advanced usage (e.g. focus traps within focus traps), you can also pause a focus trap's behavior without deactivating it entirely, then unpause at will.
Installation
npm install focus-trap
UMD
You can also use a UMD version published to unpkg.com
as dist/focus-trap.umd.js
and dist/focus-trap.umd.min.js
.
NOTE: The UMD build does not bundle the
tabbable
dependency. Therefore you will have to also include that one, and include it beforefocus-trap
.
<head>
<script src="https://unpkg.com/tabbable/dist/index.umd.js"></script>
<script src="https://unpkg.com/focus-trap/dist/focus-trap.umd.js"></script>
</head>
Browser Support
As old and as broad as reasonably possible, excluding browsers that are out of support or have nearly no user base.
Focused on desktop browsers, particularly Chrome, Edge, FireFox, Safari, and Opera.
Focus-trap is not officially tested on any mobile browsers or devices.
❗️ Safari: By default, Safari does not tab through all elements on a page, which alters the normal DOM-based tab order expected by focus-trap. If you use or support Safari with this library, make sure you and your users know they must enable the
Preferences > Advanced > Press Tab to highlight each item on a webpage
feature. Otherwise, your traps will not work the way you expect them to.
⚠️ Microsoft no longer supports any version of IE, so IE is no longer supported by this library.
💬 Focus-trap relies on tabbable so its browser support is at least what tabbable supports.
💬 Keep in mind that performance optimization and old browser support are often at odds, so tabbable may not always be able to use the most optimal (typically modern) APIs in all cases.
Usage
createFocusTrap(element[, createOptions])
import * as focusTrap from 'focus-trap'; // ESM
const focusTrap = require('focus-trap'); // CJS
// UMD: `focusTrap` is defined as a global on `window`
trap = focusTrap.createFocusTrap(element[, createOptions]);
Returns a new focus trap on element
(one or more "containers" of tabbable nodes that, together, form the total set of nodes that can be visited, with clicks or the tab key, within the trap).
element
can be:
- a DOM node (the focus trap itself);
- a selector string (which will be passed to
document.querySelector()
to find the DOM node); or - an array of DOM nodes or selector strings (where the order determines where the focus will go after the last tabbable element of a DOM node/selector is reached).
A focus trap must have at least one container with at least one tabbable/focusable node in it to be considered valid. While nodes can be added/removed at runtime, with the trap adjusting to added/removed tabbable nodes, an error will be thrown if the trap ever gets into a state where it determines none of its containers have any tabbable nodes in them and the
fallbackFocus
option does not resolve to an alternate node where focus can go.
createOptions
- onActivate
{() => void}
: A function that will be called before sending focus to the target element upon activation. - onPostActivate
{() => void}
: A function that will be called after sending focus to the target element upon activation. - checkCanFocusTrap
{(containers: Array<HTMLElement | SVGElement>) => Promise<void>}
: Animated dialogs have a small delay between whenonActivate
is called and when the focus trap is focusable.checkCanFocusTrap
expects a promise to be returned. When that promise settles (resolves or rejects), focus will be sent to the first tabbable node (in tab order) in the focus trap (or the node configured in theinitialFocus
option). - onDeactivate
{() => void}
: A function that will be called before returning focus to the node that had focus prior to activation (or configured with thesetReturnFocus
option) upon deactivation. - onPostDeactivate
{() => void}
: A function that will be called after the trap is deactivated, afteronDeactivate
. If thereturnFocus
deactivation option was set, it will be called after returning focus to the node that had focus prior to activation (or configured with thesetReturnFocus
option) upon deactivation; otherwise, it will be called after deactivation completes. - checkCanReturnFocus
{(trigger: HTMLElement | SVGElement) => Promise<void>}
: An animated trigger button will have a small delay between whenonDeactivate
is called and when the focus is able to be sent back to the trigger.checkCanReturnFocus
expects a promise to be returned. When that promise settles (resolves or rejects), focus will be sent to to the node that had focus prior to the activation of the trap (or the node configured in thesetReturnFocus
option). - initialFocus
{HTMLElement | SVGElement | string | false | (() => HTMLElement | SVGElement | string | false)}
: By default, when a focus trap is activated the first element in the focus trap's tab order will receive focus. With this option you can specify a different element to receive that initial focus. Can be a DOM node, or a selector string (which will be passed todocument.querySelector()
to find the DOM node), or a function that returns any of these. You can also set this option tofalse
(or to a function that returnsfalse
) to prevent any initial focus at all when the trap activates.- 💬 Setting this option to
false
(or a function that returnsfalse
) will prevent thefallbackFocus
option from being used. - ⚠️ See warning below about Shadow DOM and selector strings.
- 💬 Setting this option to
- fallbackFocus
{HTMLElement | SVGElement | string | () => HTMLElement | SVGElement | string}
: By default, an error will be thrown if the focus trap contains no elements in its tab order. With this option you can specify a fallback element to programmatically receive focus if no other tabbable elements are found. For example, you may want a popover's<div>
to receive focus if the popover's content includes no tabbable elements. Make sure the fallback element has a negativetabindex
so it can be programmatically focused. The option value can be a DOM node, a selector string (which will be passed todocument.querySelector()
to find the DOM node), or a function that returns any of these.- 💬 If
initialFocus
isfalse
(or a function that returnsfalse
), this function will not be called when the trap is activated, and no element will be initially focused. This function may still be called while the trap is active if things change such that there are no longer any tabbable nodes in the trap. - ⚠️ See warning below about Shadow DOM and selector strings.
- 💬 If
- escapeDeactivates
{boolean} | (e: KeyboardEvent) => boolean)
: Default:true
. Iffalse
or returnsfalse
, theEscape
key will not trigger deactivation of the focus trap. This can be useful if you want to force the user to make a decision instead of allowing an easy way out. Note that if a function is given, it's only called if the ESC key was pressed. - clickOutsideDeactivates
{boolean | (e: MouseEvent | TouchEvent) => boolean}
: Iftrue
or returnstrue
, a click outside the focus trap will immediately deactivate the focus trap and allow the click event to do its thing (i.e. to pass-through to the element that was clicked). This option takes precedence overallowOutsideClick
when it's set totrue
. Default:false
.- 💬 If a function is provided, it will be called up to twice (but only if the click occurs outside the trap's containers): First on the
mousedown
(ortouchstart
on mobile) event and, iftrue
was returned, again on theclick
event. It will get the same node each time, and it's recommended that the returned value is also the same each time. Be sure to check the event type if the double call is an issue in your code. - ⚠️ If you're using a password manager such as 1Password, where the app adds a clickable icon to all fillable fields, you should avoid using this option, and instead use the
allowOutsideClick
option to better control exactly when the focus trap can be deactivated. The clickable icons are usually positioned absolutely, floating on top of the fields, and therefore not part of the container the trap is managing. When using theclickOutsideDeactivates
option, clicking on a field's 1Password icon will likely cause the trap to be unintentionally deactivated.
- 💬 If a function is provided, it will be called up to twice (but only if the click occurs outside the trap's containers): First on the
- allowOutsideClick
{boolean | (e: MouseEvent | TouchEvent) => boolean}
: If set and is or returnstrue
, a click outside the focus trap will not be prevented (letting focus temporarily escape the trap, without deactivating it), even ifclickOutsideDeactivates=false
. Default:false
.- 💬 If this is a function, it will be called up to twice on every click (but only if the click occurs outside the trap's containers): First on
mousedown
(ortouchstart
on mobile), and then on the actualclick
if the function returnedtrue
on the first event. Be sure to check the event type if the double call is an issue in your code. - 💡 When
clickOutsideDeactivates=true
, this option is ignored (i.e. if it's a function, it will not be called). - Use this option to control if (and even which) clicks are allowed outside the trap in conjunction with
clickOutsideDeactivates=false
.
- 💬 If this is a function, it will be called up to twice on every click (but only if the click occurs outside the trap's containers): First on
- returnFocusOnDeactivate
{boolean}
: Default:true
. Iffalse
, when the trap is deactivated, focus will not return to the element that had focus before activation. - setReturnFocus
{HTMLElement | SVGElement | string | (previousActiveElement: HTMLElement | SVGElement) => HTMLElement | SVGElement | string | false}
: By default, on deactivation, ifreturnFocusOnDeactivate=true
(or ifreturnFocus=true
in the deactivation options), focus will be returned to the element that was focused just before activation. With this option, you can specify another element to programmatically receive focus after deactivation. It can be a DOM node, a selector string (which will be passed todocument.querySelector()
to find the DOM node upon deactivation), or a function that returns any of these to call upon deactivation (i.e. the selector and function options are only executed at the time the trap is deactivated). Can also befalse
(or returnfalse
) to leave focus where it is at the time of deactivation.- 💬 Using the selector or function options is a good way to return focus to a DOM node that may not exist at the time the trap is activated.
- ⚠️ See warning below about Shadow DOM and selector strings.
- preventScroll
{boolean}
: By default, focus() will scroll to the element if not in viewport. It can produce unintended effects like scrolling back to the top of a modal. If set totrue
, no scroll will happen. - delayInitialFocus
{boolean}
: Default:true
. Delays the autofocus to the next execution frame when the focus trap is activated. This prevents elements within the focusable element from capturing the event that triggered the focus trap activation. - document {Document}: Default:
window.document
. Document where the focus trap will be active. This allows to use FocusTrap in an iFrame context. - tabbableOptions: (optional) tabbable options configurable on FocusTrap (all the common options).
- ⚠️ See notes about testing in JSDom (e.g. using Jest).
- trapStack (optional)
{Array<FocusTrap>}
: Define the global trap stack. This makes it possible to share the same stack in multiple instances offocus-trap
in the same page such that auto-activation/pausing of traps is properly coordinated among all instances as activating a trap when another is already active should result in the other being auto-paused. By default, each instance will have its own internal stack, leading to conflicts if they each try to trap the focus at the same time. - isKeyForward
{(event: KeyboardEvent) => boolean}
: (optional) Determines if the given keyboard event is a "tab forward" event that will move the focus to the next trapped element in tab order. Defaults to theTAB
key. Use this to override the trap's behavior if you want to use arrow keys to control keyboard navigation within the trap, for example. Also seeisKeyBackward()
option.- ⚠️ Using this option will not automatically prevent use of the
TAB
key as the browser will continue to respond to it by moving focus forward because that's what using theTAB
key does in a browser, but it will no longer respect the trap's container edges as it normally would. You will need to add your ownkeydown
handler to callpreventDefault()
on aTAB
key event if you want to completely suppress the use of theTAB
key.
- ⚠️ Using this option will not automatically prevent use of the
- isKeyBackward
{(event: KeyboardEvent) => boolean}
: (optional) Determines if the given keyboard event is a "tab backward" event that will move the focus to the previous trapped element in tab order. Defaults to theSHIFT+TAB
key. Use this to override the trap's behavior if you want to use arrow keys to control keyboard navigation within the trap, for example. Also seeisKeyForward()
option.- ⚠️ Using this option will not automatically prevent use of the
SHIFT+TAB
key as the browser will continue to respond to it by moving focus backward because that's what using theSHIFT+TAB
key sequence does in a browser, but it will no longer respect the trap's container edges as it normally would. You will need to add your ownkeydown
handler to callpreventDefault()
on aTAB
key event if you want to completely suppress the use of theSHIFT+TAB
key sequence.
- ⚠️ Using this option will not automatically prevent use of the
Shadow DOM
Selector strings
⚠️ Beware that putting a focus-trap inside an open Shadow DOM means you must either:
- Not use selector strings for options that support these (because nodes inside Shadow DOMs, even open shadows, are not visible via
document.querySelector()
); OR - You must use the
document
option to configure the focus trap to use your shadow host element as its document. The downside of this option is that, while selector queries on nodes inside your trap will now work, the trap will not prevent focus from being set on nodes outside your Shadow DOM, which is the same drawback as putting a focus trap inside an iframe.
Closed shadows
If you have closed shadow roots that you would like considered for tabbable/focusable nodes, use the tabbableOptions.getShadowRoot
option to provide Tabbable (used internally) with a reference to a given node's shadow root so that it can be searched for candidates.
trap.active
trap.active: boolean
True if the trap is currently active.
trap.paused
trap.paused: boolean
True if the trap is currently paused.
trap.activate()
trap.activate([activateOptions]) => FocusTrap
Activates the focus trap, adding various event listeners to the document.
If focus is already within it the trap, it remains unaffected. Otherwise, focus-trap will try to focus the following nodes, in order:
createOptions.initialFocus
- The first tabbable node in the trap
createOptions.fallbackFocus
If none of the above exist, an error will be thrown. You cannot have a focus trap that lacks focus.
Returns the trap
.
activateOptions
:
These options are used to override the focus trap's default behavior for this particular activation.
- onActivate
{() => void}
: Default: whatever you chose forcreateOptions.onActivate
.null
orfalse
are the equivalent of anoop
. - onPostActivate
{() => void}
: Default: whatever you chose forcreateOptions.onPostActivate
.null
orfalse
are the equivalent of anoop
. - checkCanFocusTrap
{(containers: Array<HTMLElement | SVGElement>) => Promise<void>}
: Default: whatever you chose forcreateOptions.checkCanFocusTrap
.
trap.deactivate()
trap.deactivate([deactivateOptions]) => FocusTrap
Deactivates the focus trap.
Returns the trap
.
deactivateOptions
:
These options are used to override the focus trap's default behavior for this particular deactivation.
- returnFocus
{boolean}
: Default: whatever you set forcreateOptions.returnFocusOnDeactivate
. Iftrue
, then thesetReturnFocus
option (specified when the trap was created) is used to determine where focus will be returned. - onDeactivate
{() => void}
: Default: whatever you set forcreateOptions.onDeactivate
.null
orfalse
are the equivalent of anoop
. - onPostDeactivate
{() => void}
: Default: whatever you set forcreateOptions.onPostDeactivate
.null
orfalse
are the equivalent of anoop
. - checkCanReturnFocus
{(trigger: HTMLElement | SVGElement) => Promise<void>}
: Default: whatever you set forcreateOptions.checkCanReturnFocus
. Not called if thereturnFocus
option is falsy.trigger
is either the originally focused node prior to activation, or the result of thesetReturnFocus
configuration option.
trap.pause()
trap.pause() => FocusTrap
Pause an active focus trap's event listening without deactivating the trap.
If the focus trap has not been activated, nothing happens.
Returns the trap
.
Any onDeactivate
callback will not be called, and focus will not return to the element that was focused before the trap's activation. But the trap's behavior will be paused.
This is useful in various cases, one of which is when you want one focus trap within another. demo-six
exemplifies how you can implement this.
trap.unpause()
trap.unpause() => FocusTrap
Unpause an active focus trap. (See pause()
, above.)
Focus is forced into the trap just as described for focusTrap.activate()
.
If the focus trap has not been activated or has not been paused, nothing happens.
Returns the trap
.
trap.updateContainerElements()
trap.updateContainerElements() => FocusTrap
Update the element(s) that are used as containers for the focus trap.
When you call the function createFocusTrap
, you pass in an element (or selector), or an array of elements (or selectors) to keep the focus within. This method simply allows you to update which elements to keep the focus within.
A use case for this is found in focus-trap-react, where React ref
's may not be initialized yet, but when they are you want to have them be a container element.
Returns the trap
.
Examples
Read code in docs/
and see how it works.
Here's generally what happens in default.js
(the "default behavior" demo):
const { createFocusTrap } = require('../../index');
const container = document.getElementById('default');
const focusTrap = createFocusTrap('#default', {
onActivate: () => container.classList.add('is-active'),
onDeactivate: () => container.classList.remove('is-active'),
});
document
.getElementById('activate-default')
.addEventListener('click', focusTrap.activate);
document
.getElementById('deactivate-default')
.addEventListener('click', focusTrap.deactivate);
Other details
One at a time
Only one focus trap can be listening at a time. If a second focus trap is activated the first will automatically pause. The first trap is unpaused and again traps focus when the second is deactivated.
Focus trap manages a queue of traps: if A activates; then B activates, pausing A; then C activates, pausing B; when C then deactivates, B is unpaused; and when B then deactivates, A is unpaused.
Use predictable elements for the first and last tabbable elements in your trap
The focus trap will work best if the first and last focusable elements in your trap are simple elements that all browsers treat the same, like buttons and inputs.**
Tabbing will work as expected with trickier, less predictable elements — like iframes, shadow trees, audio and video elements, etc. — as long as they are between more predictable elements (that is, if they are not the first or last tabbable element in the trap).
This limitation is ultimately rooted in browser inconsistencies and inadequacies, but it comes to focus-trap through its dependency Tabbable. You can read about more details in the Tabbable documentation.
Your trap should include a tabbable element or a focusable container
You can't have a focus trap without focus, so an error will be thrown if you try to initialize focus-trap with an element that contains no tabbable nodes.
If you find yourself in this situation, you should give you container tabindex="-1"
and set it as initialFocus
or fallbackFocus
. A couple of demos illustrate this.
Development
Because of the nature of the functionality, involving keyboard and click and (especially) focus events, JavaScript unit tests don't make sense. After all, JSDom does not fully support focus events. Since the demo was developed to also be the test, we use Cypress to automate running through all demos in the demo page.
Help
Testing in JSDom
⚠️ JSDom is not officially supported. Your mileage may vary, and tests may break from one release to the next (even a patch or minor release).
This topic is just here to help with what we know may affect your tests.
In general, a focus trap is best tested in a full browser environment such as Cypress, Playwright, or Nightwatch where a full DOM is available.
Sometimes, that's not entirely desirable, and depending on what you're testing, you may be able to get away with using JSDom (e.g. via Jest), but you'll have to configure your traps using the tabbableOptions.displayCheck: 'none'
option.
See Testing tabbable in JSDom for more details.
Contributing
See CONTRIBUTING.
Contributors
In alphabetical order: