@aurolabs/auro-back-to-top v1.1.0

Back-to-top

<auro-back-to-top> is a HTML custom element for the purpose of helping visitors quickly return to page top.

UI development browser support

For the most up to date information on UI development browser support

Install

$ npm i @aurolabs/auro-back-to-top

Installing as a direct, dev or peer dependency is up to the user installing the package. If you are unsure as to what type of dependency you should use, consider reading this stack overflow answer.

Design Token CSS Custom Property dependency

The use of any Auro custom element has a dependency on the Auro Design Tokens.

CSS Custom Property fallbacks

CSS custom properties are not supported in older browsers. For this, fallback properties are pre-generated and included with the npm.

Any update to the Auro Design Tokens will be immediately reflected with browsers that support CSS custom properties, legacy browsers will require updated components with pre-generated fallback properties.

Define dependency in project component

Defining the component dependency within each component that is using the <auro-back-to-top> component.

import "@aurolabs/auro-back-to-top";

Reference component in HTML

<auro-back-to-top></auro-back-to-top>

Install bundled assets from CDN

In cases where the project is not able to process JS assets, there are pre-processed assets available for use. Two bundles are available -- auro-back-to-top__bundled.js for modern browsers and auro-back-to-top__bundled.es5.js for legacy browsers (including IE11).

Since the legacy bundle includes many polyfills that are not needed by modern browsers, we recommend you load these bundles using differential serving so that the browser only loads the bundle it needs. To accomplish this, the script tag for the modern bundle should have type="module" and the script tag for the legacy bundle should have the nomodule attribute. See the example below.

NOTE: Be sure to replace @latest in the URL with the version of the asset you want. @latest is NOT aware of any MAJOR releases, use at your own risk.

<link rel="stylesheet" href="https://unpkg.com/@alaskaairux/design-tokens@latest/dist/tokens/CSSCustomProperties.css" />
<link rel="stylesheet" href="https://unpkg.com/@alaskaairux/webcorestylesheets@latest/dist/bundled/essentials.css" />

<script src="https://unpkg.com/@aurolabs/auro-back-to-top@latest/dist/auro-back-to-top__bundled.js" type="module"></script>
<script src="https://unpkg.com/@aurolabs/auro-back-to-top@latest/dist/auro-back-to-top__bundled.es5.js" nomodule></script>

auro-back-to-top use cases

The <auro-back-to-top> element should be used in situations where users may:

• informational pages with many sections
• pages with infinite scroll

API Code Examples

Default (fixed positioning):

<auro-back-to-top focus-id="top"></auro-back-to-top>

The most important--and required--attribute to this element is focus-id. This is the id of an focusable element at the top of the page. When the trigger button is clicked to go back to top, the element will shift focus to the target element and scroll to its top position. A useful way to think of this is a reverse of the "Skip to main" affordance.

Anchors or buttons are examples of focusable elements, but more likely the target is a <div>, <main>, <section> or other non-focusable element. To these, you'll need to add the tabindex attribute with a value of -1. This will allow the element to receive focus so your user can resume tabbing from the top of the page, but it will keep the target element out of the default tab order so users don't stumble into it at the start of the page.

<main id="top" tabindex="-1">
    ...
    <auro-back-to-top focus-id="top"></auro-back-to-top>
</main>

Adjust how soon or delayed the button shows either by where you include the element in your document or with the rootmargintop property:

<!-- delay showing the button until after user scrolls 3vh + 1vh (reference element out-of-screen) -->
<auro-back-to-top focus-id="top" offset="3vh"></auro-back-to-top>

To display inline:

<auro-back-to-top focus-id="top" inline></auro-back-to-top>

For i18n support:

<auro-back-to-top focus-id="top">volver arriba</auro-back-to-top>

You can customize what renders in the button:

<auro-back-to-top focus-id="top" inline>zoom zoom! 🚀</auro-back-to-top>

Possible issues and workarounds

Issues with auro-back-to-top element and its fixed-position button may trace back to stacking context. For a good time learning about how the browser decides where to position elements and stacking contexts, the MDN documentation on position is a great start.

The button does not become visible at the expected scroll height

To know when to show and hide the fixed button, auro-back-to-top uses a reference element positioned absolutely to top. Placing the auro-back-to-top as the last content node in the body is encouraged. If not possible, look for parent nodes with position set other than the default, static.

The button scrolls under elements on the page

The fixed button applies a high z-index to improve its odds of rendering above content but it can still lose. The suggestion above can help here, too: placing the auro-back-to-top as the last content node in the body. If not possible, inspect the position and z-index styles applied to elements it scrolls under, use negative z-index if necessary to allow the button to scroll over top.

Why is my page too tall?

If you set a high offset, for example offset="42vh", this will increase the total height of your content. Set offset value reasonably and check at different breakpoints so that it never calculates as taller than the content height.

Development

In order to develop against this project, if you are not part of the core team, you will be required to fork the project prior to submitting a pull request.

Please be sure to review the contribution guidelines for this project. Please make sure to pay special attention to the conventional commits section of the document.

Start development environment

Once the project has been cloned to your local resource and you have installed all the dependencies you will need to open two different shell sessions. One is for the npm tasks, the second is to run the server.

// shell terminal one
$ npm run dev

// shell terminal two
$ npm run serve

Open localhost:8000

Testing

Automated tests are required for every Auro component. See .\test\auro-back-to-top.test.js for the tests for this component. Run npm test to run the tests and check code coverage. Tests must pass and meet a certain coverage threshold to commit. See the testing documentation for more details.

Demo deployment

To deploy a demo version of the component for review, run npm run demo:build to create a ./build directory that can be pushed to any static server.