This is a polyfill for the proposed JavaScript visual viewport segments for foldable and dual-screen devices.

Web developers targeting foldable devices want to be able to effectively lay out the content in a window that spans multiple displays. In some cases such as Canvas context or very unpredictable layouts, developers will need a JavaScript APIs to learn about available screens, their segments and natural boundaries.

This polyfill is only useful for the desktop or for devices not supporting the API. If you run it on the Surface Duo the polyfill will not do anything.

The segments method will return an array of screen segments, each segment is an object containing width, height, top ,left, right and bottom properties (aka segment's bounding rects)

const segments = window.visualViewport.segments();

console.log(screenSegments.length) // 2 in the example above

This polyfill is packaged as a JavaScript module. It is available on NPM over here.

To install the polyfill just run:

npm install --save viewportsegments-polyfill

Then you can include it in your project:

<script type="module" src="/path/to/modules/viewportsegments-polyfill.js"></script>

or in your JavaScript source file

import "/path/to/modules/viewportsegments-polyfill/viewportsegments-polyfill.js";

That's it. See the demo/basic directory for examples.

In order to change the display configuration, you can use the polyfill together with an emulator or you can change the settings manually. The settings are stored across sessions.

You can update values such as horizontalViewportSegments, verticalViewportSegments, foldSize and browserShellSize by importing the FoldablesFeature object. You can also subscribe to the 'change' event to be notified whenever the environment variables change. That can happen due to window resizes or because the configuration values were changed programmatically.

  import { FoldablesFeature } from '/path/to/modules/viewportsegments-polyfill/viewportsegments-polyfill.js';

  const foldablesFeat = new FoldablesFeature;

  // Add an event listener.
  foldablesFeat.onchange = () => console.log("change");

    // Add as many event listeners as you want.
  foldablesFeat.addEventListener('change', () => console.log("change"));

  // Change a single value; results in one update (one 'change' event firing).
  foldablesFeat.foldSize = 20;

  // Change multiple values by assignment; results in one update.
  Object.assign(foldablesFeat, { foldSize: 50, verticalViewportSegments: "2"});

  // Change multiple values in one scope; results in one update
  (function() { foldablesFeat.foldSize = 100; foldablesFeat.verticalViewportSegments = "2" })();

Located here.

There are unfortunately no web-platform-tests available yet.

Check GitHub here.

• Explainer - a document explaining how this feature was designed and how it fits together with other APIs.
• CSS Viewport Segment Media Feature Polyfill