Trap Plugin

Alpine's Trap plugin allows you to conditionally trap focus inside an element.

This is useful for modals and other dialog elements.

Installation

You can use this plugin by either including it from a <script> tag or installing it via NPM:

Via CDN

You can include the CDN build of this plugin as a <script> tag, just make sure to include it BEFORE Alpine's core JS file.

<!-- Alpine Plugins -->
<script defer src="https://unpkg.com/@alpinejs/[email protected]/dist/cdn.min.js"></script>
 
<!-- Alpine Core -->
<script defer src="https://unpkg.com/[email protected]/dist/cdn.min.js"></script>

Via NPM

You can install Trap from NPM for use inside your bundle like so:

npm install @alpinejs/trap

Then initialize it from your bundle:

import Alpine from 'alpinejs'
import trap from '@alpinejs/trap'
 
Alpine.plugin(trap)
 
...

x-trap

The primary API for using this plugin is the x-trap directive.

x-trap accepts a JS expression. If the result of that expression is true, then the focus will be trapped inside that element until the expression becomes false, then at that point, focus will be returned to where it was previously.

For example:

<div x-data="{ open: false }">
<button @click="open = true">Open Dialog</button>
 
<span x-show="open" x-trap="open">
<p>...</p>
 
<input type="text" placeholder="Some input...">
 
<input type="text" placeholder="Some other input...">
 
<button @click="open = false">Close Dialog</button>
</span>
</div>
Focus is now "trapped" inside this dialog, meaning you can only click/focus elements within this yellow dialog. If you press tab repeatedly, the focus will stay within this dialog.

Nesting dialogs

Sometimes you may want to nest one dialog inside another. x-trap makes this trivial and handles it automatically.

x-trap keeps track of newly "trapped" elements and stores the last actively focused element. Once the element is "untrapped" then the focus will be returned to where it was originally.

This mechanism is recursive, so you can trap focus within an already trapped element infinite times, then "untrap" each element successively.

Here is nesting in action:

<div x-data="{ open: false }">
<button @click="open = true">Open Dialog</button>
 
<span x-show="open" x-trap="open">
 
...
 
<div x-data="{ open: false }">
<button @click="open = true">Open Nested Dialog</button>
 
<span x-show="open" x-trap="open">
 
...
 
<button @click="open = false">Close Nested Dialog</button>
</span>
</div>
 
<button @click="open = false">Close Dialog</button>
</span>
</div>
Focus is now "trapped" inside this nested dialog. You cannot focus anything inside the outer dialog while this is open. If you close this dialog, focus will be returned to the last known active element.

Modifiers

.inert

When building things like dialogs/modals, it's recommended to hide all the other elements on the page from screenreaders when trapping focus.

By adding .inert to x-trap, when focus is trapped, all other elements on the page will receive aria-hidden="true" attributes, and when focus trapping is disabled, those attributes will also be removed.

<!-- When `open` is `false`: -->
<body x-data="{ open: false }">
<div x-trap.inert="open" ...>
...
</div>
 
<div>
...
</div>
</body>
 
<!-- When `open` is `true`: -->
<body x-data="{ open: true }">
<div x-trap.inert="open" ...>
...
</div>
 
<div aria-hidden="true">
...
</div>
</body>

.noscroll

When building dialogs/modals with Alpine, it's recommended that you disable scrollling for the surrounding content when the dialog is open.

x-trap allows you to do this automatically with the .noscroll modifiers.

By adding .noscroll, Alpine will remove the scrollbar from the page and block users from scrolling down the page while a dialog is open.

For example:

<div x-data="{ open: false }">
<button>Open Dialog</button>
 
<div x-show="open" x-trap.noscroll="open">
Dialog Contents
 
<button @click="open = false">Close Dialog</button>
</div>
</div>
Dialog Contents

Notice how you can no longer scroll on this page while this dialog is open.

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