Fragment Plugin

A swup plugin for dynamically replacing containers based on rules 🧩

Selectively replace containers instead of the main swup containers, based on custom rules
Improve orientation by animating only the parts of the page that have actually changed
Give your site the polish and snappiness of a single-page app

Use cases

All of the following scenarios require updating only a small content fragment instead of performing a full page transition:

a filter UI that live-updates its list of results on every interaction
a detail overlay that shows on top of the currently open content
a tab group that should update only itself when selecting one of the tabs

If you are looking for selectively replacing forms on submission, you should have a look at Forms Plugin.

Demo

See the plugin in action in this interactive demo

Installation
How it works
Example
Options
How rules are matched
How fragment containers are found
Advanced use cases
Skip out/in animations using <template>
Modals as children of transformed parents
Modals and Accessibility
API Methods

Installation

Install the plugin from npm and import it into your bundle.

npm install @swup/fragment-plugin

npm install @swup/fragment-plugin

import SwupFragmentPlugin from '@swup/fragment-plugin';

import SwupFragmentPlugin from '@swup/fragment-plugin';

Or include the minified production file from a CDN:

<script src="https://unpkg.com/@swup/fragment-plugin@1"></script>

<script src="https://unpkg.com/@swup/fragment-plugin@1"></script>

How it works

When a visit is determined to be a fragment visit, the plugin will:

update only the contents of the elements matching the rule's containers
not update the default containers replaced on all other visits
wait for CSS transitions on those fragment elements using scoped animations
preserve the current scroll position upon navigation
add a to-[name] class to the elements if the current rule has a name key
ignore elements that already match the current visit's URL

Imagine a website with a /users/ page that displays a list of users. Above the user list, there is a filter UI to choose which users to display. Selecting a filter will trigger a visit to the narrowed-down user list at /users/filter/x/. The only part that has changed is the list of users, so that's what we'd like to replace and animate instead of the whole content container.

<body>
  <header>Website</header>
  <main id="swup" class="transition-main" class="transition-main">
    <h1>Users</h1>
    <!-- A list of filters for the users: selecting one will update the list below -->
    <ul>
      <a href="/users/filter/1/">Filter 1</a>
      <a href="/users/filter/2/">Filter 2</a>
      <a href="/users/filter/3/">Filter 2</a>
    </ul>
    <!-- The list of users, filtered by the criteria above -->
    <ul id="users">
      <li><a href="/user/1/">User 1</a></li>
      <li><a href="/user/2/">User 2</a></li>
      <li><a href="/user/3/">User 3</a></li>
    </ul>
  </main>
</body>

<body>
  <header>Website</header>
  <main id="swup" class="transition-main" class="transition-main">
    <h1>Users</h1>
    <!-- A list of filters for the users: selecting one will update the list below -->
    <ul>
      <a href="/users/filter/1/">Filter 1</a>
      <a href="/users/filter/2/">Filter 2</a>
      <a href="/users/filter/3/">Filter 2</a>
    </ul>
    <!-- The list of users, filtered by the criteria above -->
    <ul id="users">
      <li><a href="/user/1/">User 1</a></li>
      <li><a href="/user/2/">User 2</a></li>
      <li><a href="/user/3/">User 3</a></li>
    </ul>
  </main>
</body>

Using Fragment Plugin, we can update only the #users list when clicking one of the filters. The plugin expects an array of rules to recognize and handle fragment visits:

const swup = new Swup({
  plugins: [
    new SwupFragmentPlugin({
      rules: [
        {
          from: '/users/:filter?',
          to: '/users/:filter?',
          containers: ['#users']
        }
      ]
    })
  ]
});

const swup = new Swup({
  plugins: [
    new SwupFragmentPlugin({
      rules: [
        {
          from: '/users/:filter?',
          to: '/users/:filter?',
          containers: ['#users']
        }
      ]
    })
  ]
});

Now we can add custom animations for our fragment rule:

/*
* The default animation, for visits without matching fragment rules
*/
html.is-changing .transition-main {
  transition: opacity 250ms;
  opacity: 1;
}
html.is-animating .transition-main {
  opacity: 0;
}

/*
* The animation when filtering users
*/
#users.is-changing {
  transition: opacity 250ms;
}
#users.is-animating {
  opacity: 0;
}

/*
* The default animation, for visits without matching fragment rules
*/
html.is-changing .transition-main {
  transition: opacity 250ms;
  opacity: 1;
}
html.is-animating .transition-main {
  opacity: 0;
}

/*
* The animation when filtering users
*/
#users.is-changing {
  transition: opacity 250ms;
}
#users.is-animating {
  opacity: 0;
}

Options

/** A path to match URLs against */
type Path = string | RegExp | Array<string | RegExp>;

/** A fragment rule */
export type Rule = {
  from: Path;
  to: Path;
  containers: string[];
  name?: string;
  scroll?: boolean | string;
  focus?: boolean | string;
  if?: Predicate;
};

/** The plugin options */
export type Options = {
  rules: Rule[];
  debug?: boolean;
};

/** A path to match URLs against */
type Path = string | RegExp | Array<string | RegExp>;

/** A fragment rule */
export type Rule = {
  from: Path;
  to: Path;
  containers: string[];
  name?: string;
  scroll?: boolean | string;
  focus?: boolean | string;
  if?: Predicate;
};

/** The plugin options */
export type Options = {
  rules: Rule[];
  debug?: boolean;
};

`rules`

The rules that define whether a visit will be considered a fragment visit. Each rule consists of mandatory from and to URL paths, an array of selectors containers, as well as an optional name of this rule to allow scoped styling.

The rule's from/to paths are converted to a regular expression by path-to-regexp and matched against the current browser URL. If you want to create an either/or path, you can also provide an array of paths, for example:

{
  rules: [
    {
      from: ['/users', '/users/:filter?'],
      to: ['/users', '/users/:filter?'],
      containers: ['#user-list']
    }
  ];
}

{
  rules: [
    {
      from: ['/users', '/users/:filter?'],
      to: ['/users', '/users/:filter?'],
      containers: ['#user-list']
    }
  ];
}

`rule.from`

Required, Type: string | string[] – The path(s) to match against the previous URL

`rule.to`

Required, Type: string | string[] – The path(s) to match against the next URL

`rule.containers`

Required, Type: string[] – Selectors of containers to be replaced if the visit matches.

Notes

only IDs and no nested selectors are allowed. #my-element is valid, while .my-element or #wrap #child both will throw an error.
if any of the selectors in containers doesn't return a match in the current document, the rule will be skipped.
Fragment elements must either match a swup container or be a descendant of one of them

`rule.name`

Optional, Type: string – A name for this rule to allow scoped styling, ideally in kebab-case

`rule.scroll`

Optional, Type: boolean | string – By default, scrolling will be disabled for fragment visits. Using this option, you can re-enable it for selected visits:

true will scroll to the top
'#my-element' will scroll to the first element matching the selector

`rule.focus`

Optional, Type: boolean | string – If you have Accessibility Plugin installed, you can adjust which element to focus for the visit as described here.

`rule.if`

Optional, Type: (visit) => boolean – A predicate function that allows for fine-grained control over the matching behavior of a rule. The function receives the current visit as a parameter. If the function returns false, the related rule is being skipped for the current visit, even if it matches the current route.

`debug`

Optional, Type: boolean, Default false. Set to true for debug information in the console.

{
  debug: true;
}

{
  debug: true;
}

How rules are matched

The first matching rule in your rules array will be used for the current visit
If no rule matches the current visit, the default content containers defined in swup's options will be replaced

How fragment containers are found

The containers of the matching rule need to be shared between the current and the incoming document
For each selector in the containers array, the first matching element in the DOM will be selected
If a visit isn't be considered a reload of the current page, fragment elements that already match the new URL will be ignored

Advanced use cases

Creating the rules for your fragment visits should be enough to enable dynamic updates on most sites. However, there are some advanced use cases that require adding certain attributes to the fragment elements themselves or to links on the page. These tend to be situations where overlays are involved and swup doesn't know which page the overlay was opened from.

Fragment URL

Use the data-swup-fragment-url attribute to uniquely identify fragment elements.

In scenarios where overlays are rendered on top of other content, leaving or closing the overlay to the same URL it was opened from should ideally not update the content below the overlay as nothing has changed. Fragment plugin will normally do that by keeping track of URLs. However, when swup was initialized on a subpage with a visible overlay, the plugin doesn't know which URL the overlaid content corresponds to. Hence, we need to tell it manually so it can ignore content updates without changes.

<main id="overlay">
  <h1>User 1</h1>
  <p>Lorem ipsum dolor sit amet...</p>
</main>
<section id="list"
+  data-swup-fragment-url="/users/">
  <ul>
    <li>User 1</li>
    <li>User 2</li>
    <li>User 3</li>
  </ul>
</section>

<main id="overlay">
  <h1>User 1</h1>
  <p>Lorem ipsum dolor sit amet...</p>
</main>
<section id="list"
+  data-swup-fragment-url="/users/">
  <ul>
    <li>User 1</li>
    <li>User 2</li>
    <li>User 3</li>
  </ul>
</section>

Link to fragment

Use the data-swup-link-to-fragment attribute to automatically update links pointing to a fragment.

Consider again an overlay rendered on top of other content. To implement a close button for that overlay, we could ideally point a link at the URL of the content where the overlay is closed. The fragment plugin will then handle the animation and replacing of the overlay. However, knowing where to point that link requires knowing where the current overlay was opened from.

data-swup-link-to-fragment automates that by keeping the href attribute of a link in sync with the currently tracked URL of the fragment matching the selector provided by the attribute. The code below will make sure the close button will always point at the last known URL of the #list fragment to allow seamlessly closing the overlay:

<section id="list"
  data-swup-fragment-url="/users/">
  <ul>
    <li>User 1</li>
    <li>User 2</li>
    <li>User 3</li>
  </ul>
</section>
<main id="overlay">
  <!-- `href` will be synced to the fragment URL of #list at runtime: -->
+ <a href="" data-swup-link-to-fragment="#list">Close</a>
  <h1>User 1</h1>
  <p>Lorem ipsum dolor sit amet...</p>
</main>

<section id="list"
  data-swup-fragment-url="/users/">
  <ul>
    <li>User 1</li>
    <li>User 2</li>
    <li>User 3</li>
  </ul>
</section>
<main id="overlay">
  <!-- `href` will be synced to the fragment URL of #list at runtime: -->
+ <a href="" data-swup-link-to-fragment="#list">Close</a>
  <h1>User 1</h1>
  <p>Lorem ipsum dolor sit amet...</p>
</main>

<a
+ href="/users/"
  data-swup-link-to-fragment="#list">Close</a>

<a
+ href="/users/"
  data-swup-link-to-fragment="#list">Close</a>

Skip out/in animations using `<template>`

If all elements of a visit are <template> elements, the out/in-animation will automatically be skipped. This can come in handy for modals:

{
  from: '/overview/',
  to: '/detail/:id',
  containers: ['#modal']
},
{
  from: '/detail/:id',
  to: '/overview/',
  containers: ['#modal']
}

{
  from: '/overview/',
  to: '/detail/:id',
  containers: ['#modal']
},
{
  from: '/detail/:id',
  to: '/overview/',
  containers: ['#modal']
}

<!-- /overview/: provide a <template> as a placeholder for the modal -->
<template id="modal"></template>
<main>
  <ul>
    <!-- list of items that will open in the #modal -->
  </ul>
</main>

<!-- /overview/: provide a <template> as a placeholder for the modal -->
<template id="modal"></template>
<main>
  <ul>
    <!-- list of items that will open in the #modal -->
  </ul>
</main>

<!-- /detail/1 -->
<main id="modal">
  <h1>Detail 1</h1>
</main>
<div>
  <ul>
    <!-- list of items that will open in the #modal -->
  </ul>
</div>

<!-- /detail/1 -->
<main id="modal">
  <h1>Detail 1</h1>
</main>
<div>
  <ul>
    <!-- list of items that will open in the #modal -->
  </ul>
</div>

Modals as children of `transform`ed parents

Suppose you have an overlay that you want to present like a modal, above all other content:

<div id="swup" class="transition-main" class="transition-main">
  <!-- This should be placed above everything else, like a modal -->
  <main id="user" class="modal">
    <h1>User 1</h1>
    <p>Lorem ipsum dolor...</p>
  </main>
  <!-- The list of users, overlayed by the modal above -->
  <section>
    <ul>
      <li><a href="/user/1/">User 1</a></li>
      <li><a href="/user/2/">User 2</a></li>
      <li><a href="/user/3/">User 3</a></li>
    </ul>
  </section>
</div>

<div id="swup" class="transition-main" class="transition-main">
  <!-- This should be placed above everything else, like a modal -->
  <main id="user" class="modal">
    <h1>User 1</h1>
    <p>Lorem ipsum dolor...</p>
  </main>
  <!-- The list of users, overlayed by the modal above -->
  <section>
    <ul>
      <li><a href="/user/1/">User 1</a></li>
      <li><a href="/user/2/">User 2</a></li>
      <li><a href="/user/3/">User 3</a></li>
    </ul>
  </section>
</div>

You might have this (minimal) CSS to make the #user appear as a modal above everything else:

.modal {
  position: fixed;
  inset: 0;
  z-index: 99999;
}

.modal {
  position: fixed;
  inset: 0;
  z-index: 99999;
}

This will work fine, until you apply a transform to one of the modal's parent elements:

html.is-changing .transition-main {
  transition:
    opacity 250ms,
    transform 250ms;
}
html.is-animating .transition-main {
  opacity: 0;
  /* `transform` will misplace the .modal's positioning during an animated page visit */
  transform: translateY(20px);
}

html.is-changing .transition-main {
  transition:
    opacity 250ms,
    transform 250ms;
}
html.is-animating .transition-main {
  opacity: 0;
  /* `transform` will misplace the .modal's positioning during an animated page visit */
  transform: translateY(20px);
}

The reason for this is that a CSS transform establishes a containing block for all descendants.

You have two options to fix this:

Don't apply CSS transforms to any of the parents of a modal
Use <dialog open> for the modal:

- <main id="overlay" class="modal">
+ <dialog open id="overlay" aria-role="article">
+   <main>
      <h1>User 1</h1>
      <p>Lorem ipsum dolor...</p>
- </main>
+   </main>
+ </dialog>

- <main id="overlay" class="modal">
+ <dialog open id="overlay" aria-role="article">
+   <main>
      <h1>User 1</h1>
      <p>Lorem ipsum dolor...</p>
- </main>
+   </main>
+ </dialog>

Fragment Plugin will detect <dialog open>-fragment elements automatically on every page view and run showModal() on them, putting them on the top layer and thus allows them to not be affected by parent element styles, anymore.

Modals and accessibility

Element order

The first <main> element in a document will be considered the main content by assistive technology. If you are using the A11y Plugin, that's also the element that will automatically be focused upon page visits. For that reason, you should always put your modal before any overlayed content, if it should be considered the primary content of a page.

Pros and cons of using a `<dialog open>` element for modals

Pros:

The modal's positioning won't be affected by transform animations on any of it's parents.
Focus trapping will be natively available for the modal without you having to do anything.

Cons:

Wrapping your <main> content inside a <dialog> will produce semantically incorrect markup. We still think it's the cleanest approach for now, until the Popover API reaches wider browser support.

API methods

Fragment plugin provides a few API functions for advanced use cases. To be able to access those, you'll need to keep a reference to the plugin during instanciation:

const fragmentPlugin = new SwupFragmentPlugin({ rules });
const swup = new Swup({ plugins: [fragmentPlugin] });
/** You can now call the plugin's public API, for example: */
fragmentPlugin.getFragmentVisit(route);

const fragmentPlugin = new SwupFragmentPlugin({ rules });
const swup = new Swup({ plugins: [fragmentPlugin] });
/** You can now call the plugin's public API, for example: */
fragmentPlugin.getFragmentVisit(route);

`getFragmentVisit(route)`

Get information about the fragment visit for a given route. Returns either FragmentVisit or undefined.

/**
 * Get information about which containers will
 * be replaced when hovering over links:
 */
document.querySelectorAll('a[href]').forEach((el) => {
  el.addEventListener('mouseenter', () => {
    const fragmentVisit = fragmentPlugin.getFragmentVisit({
      from: window.location.href, // the current URL
      to: el.href // the URL of the link
    });
    console.log(`will replace ${fragmentVisit?.containers || swup.options.containers}`);
  });
});

/**
 * Get information about which containers will
 * be replaced when hovering over links:
 */
document.querySelectorAll('a[href]').forEach((el) => {
  el.addEventListener('mouseenter', () => {
    const fragmentVisit = fragmentPlugin.getFragmentVisit({
      from: window.location.href, // the current URL
      to: el.href // the URL of the link
    });
    console.log(`will replace ${fragmentVisit?.containers || swup.options.containers}`);
  });
});

`prependRule(rule)`

Prepends a rule to the array of rules.

fragmentPlugin.prependRule({ from: '/foo/', to: '/bar/', containers: ['#foobar'] });

fragmentPlugin.prependRule({ from: '/foo/', to: '/bar/', containers: ['#foobar'] });

`appendRule(rule)`

Appends a rule to the array of rules.

fragmentPlugin.prependRule({ from: '/baz/', to: '/bat/', containers: ['#bazbat'] });

fragmentPlugin.prependRule({ from: '/baz/', to: '/bat/', containers: ['#bazbat'] });

`getRules()`

Get a clone of all registered fragment rules

console.log(fragmentPlugin.getRules());

console.log(fragmentPlugin.getRules());

`setRules(rules)`

Overwrite all fragment rules with the provided rules. This methods provides the lowest-level access to the rules. For example, you could use it to remove all rules with the name foobar:

fragmentPlugin.setRules(fragmentPlugin.getRules().filter((rule) => rule.name !== 'foobar'));

fragmentPlugin.setRules(fragmentPlugin.getRules().filter((rule) => rule.name !== 'foobar'));