reading position indicator

Small mobile friendly reading position indicator library with no external dependencies.

demo

https://codepen.io/kunukn/full/zNJqEE (version 1.0.3+)
https://codepen.io/kunukn/full/ayeMZN/ (version 2.0.0+)

about

A position indicator at the top of the page to visually display how far you have scrolled on a webpage.

Build with focus on simplicity, performance and a11y. Using transform translate for best performance. rAF for throttling scroll update and debounce for resize update.

Aria tags are used to support screen readers.

The progress element <progress> has not been used because the code gets messy with vendor prefixes and removing the default styles that comes with each browser. It gets even messier when fallback elements are added inside the progress element to support older browsers.

browser support


IE 10+ ✔	Latest ✔	Latest ✔	Latest ✔	Latest ✔

npm

https://www.npmjs.com/package/reading-position-indicator

size

js ~6kb
css <1kb

test

Tested with latest Chrome, Safari, Firefox, Edge, IE10+, iOS7+, Android 4.3+

usage

Check the dist/index.html for inspiration.

Add reference to rpi.bundle.js and rpi.bundle.css in the html page
Apply the markup structure
Init the library with JS

html structure

<head>
  ...
  <link rel="stylesheet" href="rpi.bundle.css">
  ...
</head>
<body>
  <!-- library markup -->
  <div class="rpi-progress-bar" 
    role="progressbar" 
    aria-valuemin="0" 
    aria-valuemax="100"
    aria-valuenow="0">
      <div class="rpi-progress-bar__position" aria-hidden="true"></div>
      <div class="rpi-progress-bar__percentage"></div>
  </div>
  <!-- end library markup -->
  
       ...          
       
       <script src="rpi.bundle.js"></script> <!-- library -->
       <script>new ReadingPositionIndicator().init();</script> <!-- usage -->
 </body>

minimum markup required

<div class="rpi-progress-bar">
      <div class="rpi-progress-bar__position"></div>
      <div class="rpi-progress-bar__percentage"></div>
</div>

configuration and usage example

var rpi;
setTimeout(function waitUntilDomIsReadyLoadingCustomFontsMightOffsetThis() {
  rpi = new ReadingPositionIndicator({
    rpiArea: '[data-rpi-area]', /* optional, query selector to an element */
    progressBar: { /* optional */
      show: true, /* default true */
      color: 'rgba(0, 120, 120, .5)', /* default from css */
    },
    percentage: { /* optional */
      show: true, /* default false */
      displayBeforeScroll: false, /* default false */
      opacity: .3, /* default from css */
      color: '#000', /* default from css */
    },
  }).init();
}, 200); // wait until DOM has fully rendered the article to get the calculations correct
// rpi.destroy(); // use when to be removed
// rpi.update(); // optional force update, example: DOM was updated and need to refresh the indicator

development

git clone the project or download it
npm install
npm start
open a browser and go to localhost:3333

build library into dist folder

npm run build

how does it work?

It calculate heights for viewport, document and current scroll position. If rpiArea is used then it also uses getBoundingClientRect method to calculate dom element dimension. DOM updates are only applied if data has changed since last time. The calculation is updated on scroll and resize event and the information is updated to the DOM.

license

MIT License: http://opensource.org/licenses/MIT

netopolit/reading-position-indicator