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    The Progressive User Experience Library (ProgUX) lets you progressively enhance your website or PWA based on the following criteria:

    • Users Preferences
      • Prefers Reduced Motion
      • Save Data Settings
      • Tracking Settings
    • Device Capabilities
      • CPU Capacity
      • Memory Level
    • Network
      • Connection Speed

    The libraray is using modern browser APIs to collect the data of the current session and creates a JavaScript object in the Session Storage and CSS classes in the

    . Each of these can be used to decide what features, content, web fonts, JavaScript, CSS, etc. will be delivered to the user to create a progressive user experience.

    The idea is similar to react-adapitve-hooks. However ProgUX is not limited to React and provides a simulator which makes it easy to test different settings in the developer/test mode.


    To start using ProgUX inline the code from dist/prod/bundle.js before any other JavaScript and CSS code in the

    and call the progUX() to initialise the script. If you want to override any of the configurations pass it to the function as an object.
    <script type="application/javascript">
      !function(){"use strict";const n=n=>"connection"in navigator ... // inline whole code
          sessionStorageKey: 'someOtherKeyName'

    The web performance impact to run the production code is about ~10ms (measured on a local dev environment without throtteling).


    How your application changes and adapts to the environmental constraints and capabilities is ultimately up to you. ProgUX will not perform any magic that will change your application, it simply provides each developer who uses it a snapshot with which they can make decisions.

    Ultimately how you use this is up-to-you, below we describe how you can gain access to this information.

    Once installed and the application has reloaded developers will have access to an object in the session storage as well as a number of classes to reference in the <HTML> tag.

    Session Storage Object

    The object will contain the following keys and values:

    connectionSpeed: String; // 'slow/fast/unknown'
    cpuLevel: String; // 'low/mid/high/unknown'
    memoryLevel: String; // 'low/mid/high/unknown'
    reducedMotion: Boolean;
    saveData: Boolean;
    doNotTrack: Boolean;

    CSS Classes

    The <HTML> tag will contain the following classes


    The output will look similar to this

    <html class="connectionSpeed-slow cpuLevel-low ...">

    You then have access to the classes to make decisions in your code, for example

    .connectionSpeed-slow {
      .stage-image {
        display: block;
      .stage-video {
        display: none;

    To try to limit the impact of unnecessary JavaScript checks ProgUX will only update the connectionSpeed during a user session. This is simply because we believe that this is the only one of our checks likely to change during a session.

    Development/testing Environment

    To aid developers and testers we have provided a dist/dev/dev-bundle.js and dist/dev/dev-bundle.css files that contain extra features.

    Using this script will run the checks in exactly the same way as the production script but contains a modal that allows you to change the settings on the fly.

    You can inline this script as well or use it as modules (JS). CSS you can add to your project and link to the stylesheet in the head.

    Settings Modal

    Once your application has loaded you will see a cog icon (by default in the top left of your screen), if you click the icon it will open the settings modal.


    The modal will automatically be set to reflect the current settings and to make adjustments to this you simply alter the controls to your new desired configuration and hit the 'Submit' button. This will force a page reload, the session storage object and the classes in the HTML will have been updated

    Inside the modal there is also a toggle switch to show a 'Current Status' bar.


    This is designed so that if you need to take screenshots of particular variations of the application it will be easy to identify the ProgUX settings at that time.

    The Status Bar is moveable to provide you with the best result.


    ProgUX provides a config.js file found in src/js.

    Inside the file you will find an object with the following properties

    // prod and dev
    settings: lowRAM: Number; // 0.25, 0.5, 1, 2, 4, 8
    lowCPU: Number; // > 0
    slowConnectionTypes: Array; // 'slow-2g','2g','3g', or '4g'
    sessionStorageKey: String; // 'progressiveUserSettings',
    // dev only
    sessionStorageDevKey: String; // 'progressiveUserDevSettings',
    defaultDevSettings: isDraggable: Boolean;
    mode: String; // 'closed','open'
    posTop: Number; // 20 (in px)
    posLeft: Number; // 20 (in px)

    You can use this attribute names and structure when overriding wanted attributes.

    Overriding config

    Oveeride of the default congiguration is possible by passing the object with new values for wanted properties to init function (progUX() or progUXdev())

    Overriding the values will set the thresholds tested by ProgUX in your application. For instance, by default slowConnectionTypes is set to ['slow-2g', '2g', '3g'], if you considered '3g' to not be a slow connection you could remove it.

    Overriding the sessionStorageKey will alter the name of the object saved in your session storage, etc.

    Browser Support

    Unfortunately, not all modern browsers support all the APIs, so please check support list before using and plan fallback.


    Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

    Run project locally

    To test project locally, there are 2 basic html files with integration of both production and development versions of ProgUX. To start local server run

    npm run start

    for production mode or

    npm run start-dev

    for development mode.

    If you want to do some development, there are also watchers included. To run them open a new tab next to one where server is running and run:

    npm run watch

    For any questions and issues feel free to contact us.




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