:mouse_trap: focus-svelte

Focus trap for svelte with zero dependencies.

Installation

1npm install -D focus-svelte
2# yarn add -D focus-svelte
3# pnpm add -D focus-svelte

Example

https://svelte.dev/repl/4b31b2f4a45c4ee08230f6d47d31db48

Description

focus-svelte works a bit differently than other focus traps I've encounted. Rather than using an event listener to track user activity and override the default behavior of the browser, the DOM is manipulated instead. All elements outside of an active focus trap's descendants or ancestory have their tabindex set to -1 if it was 0 or greater previously.

To keep track of changes after the trap is enabled, a MutationObserver monitors the DOM for updates. Once all focus traps are disabled or removed, the observer is stopped and the elements' properties are reset. If a focus trap later becomes active, the observer is restarted and nodes are decorated accordingly.

When a trap becomes active for the first time, the HTMLElement that is assigned focus is determined by the configuration options passed to the component or action.

• If element is assigned and is tabbable, it will be focused upon.
• If element is undefined or not tabbable and focusable is true, the HTMLElement with use:focus is granted focus.
• If neither of the previous conditions are met, focus will be placed on the first tabbable element.

Usage

There is both an action and a component that can be utilized.

Options

option	description	type	default
element	If element is assigned and is tabbable, it will be focused upon when the trap is enabled. string values will be considered a query selector.	Element | string	undefined
focusable	The HTMLElement the action is assigned to gets a tabindex of 0 when the trap becomes active	boolean	false
focusDelay	can either be a number of ms to wait or an async function that resolves (void) when the focus of an element should be set.	number | () => Promise<void>	tick
delay	Determines how long to wait before batching updates to tabIndex and ariaHidden.	number | () => Promise<void>	tick
assignAriaHidden	When a focus trap becomes enabled and is true, all elements outside of an active trap or their ancestory have their aria-hidden attribute set to "true".	boolean	false
preventScroll	sets preventScroll when focusing.	boolean	false
enabled	If true, the focus trap becomes active.	boolean	false

action

1<script>
2	import { focus } from "focus-svelte";
3	let enabled = true;
4	function toggleFocus() {
5		enabled = !enabled;
6	}
7</script>
8
9<button on:click="{toggleFocus}">{enabled ? "disable" : "enable"} focus</button>
10
11<div use:focus="{enabled}">
12	<input value={enabled ? "focus is trapped here" : "regular tabbable input"} />
13</div>
14
15<input value={enabled ? "can't tab here" : "can be tabbed into!"} />

With assignAriaHidden

1<script>
2	import { focus } from "focus-svelte";
3	let enabled = true;
4	function toggleFocus() {
5		enabled = !enabled;
6	}
7</script>
8
9<button on:click="{toggleFocus}">{enabled ? "disable" : "enable"} focus</button>
10
11<div use:focus="{{enabled, assignAriaHidden: true}}">
12	<input value={enabled ? "focus is trapped here" : "regular tabbable input"} />
13</div>
14
15<input value={enabled ? "can't tab here" : "can be tabbed into!"} />

component

1<script>
2	import { Focus } from "focus-svelte";
3	let enabled = true;
4	function toggleFocus() {
5		enabled = !enabled;
6	}
7</script>
8
9<button on:click="{toggleFocus}">{enabled ? "disable" : "enable"} focus</button>
10
11<Focus {enabled} assignAriaHidden="{true}">
12	<input value={enabled ? "focus is trapped here" : "regular tabbable input"} />
13</Focus>
14
15<input value={enabled ? "can't tab here" : "can be tabbed into!"} />

Note: As the action needs an HTMLElement, the component version wraps your content with a div.

override

If you wish to override the behavior of an element, you can set data-focus-override="true" and it will retain its original tabindex.

Contributing

Pull requests are always welcome.

License

MIT