# Evaluating Progressive Web App Accessibility for People with Disabilities
## 3 Progressive Web Apps (PWAs)  
Prior research has found that almost four fifths (79%) of internet users access the internet on their mobile devices [7]. Statistical research agencies support the statistics that mobile internet traffic as a share of total global online traffic is greater than 55.64% and that, in 2020, mobile app downloads worldwide amounted to 218 billion [8].  
Mobile devices are an indispensable part of human life nowadays. Mobile apps have been developed for every field and any need, from taking and editing photos to accessing social media, attending online meetings, and more. The incremental need for mobile apps led development companies to develop native or hybrid applications to overcome the limitations that the web as a platform imposes on mobile devices [1]. However, even mobile apps face some limitations, such as the following:  
* Platform-specific applications;
* Devices' resources consumption;
* Multiplatform updates;
* Search engine optimization;
* Challenging app store optimization.  
To overcome these limitations, in 2015, Google introduced a new technology, namely, PWAs, which are web applications built with modern APIs to deliver enhanced capabilities, reliability, and installability while reaching anyone, anywhere, and on any device with a single codebase [2]. As browsers become more modern, an increasing number of features become available to end users. This is known as progressive enhancement [5]. PWAs try to solve UX and user offline use. Moreover, they combine the advantages of apps and the web, such as being progressive, reliable, responsive, offline functional, interactive, installable, and notifiable [9]. PWAs are based on three main pillars:  
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* Capable: new and upcoming APIs are more capable than ever, introducing new capabilities, from file system access to app badging.
* Reliable: PWAs are reliable, fast, and dependable, regardless of network speed.
* Installable: PWAs run as apps on a user's home screen without any browser tab. Furthermore, PWAs' main characteristics are as follows:
* Progressive: using service workers and a web app manifest, PWAs work on every modern browser.
* App-like: they use the app-shell model to provide app-style navigations and interactions [10].
* Installable: installed PWAs appear on the launch surfaces of any devices, such as the Mac OS X Applications folder and Spotlight function.
* Independently installed: they bypass App Store and Google Play installations.
* Responsive: PWAs are responsive and accessible from any platform and browser.
* Independent of connectivity: they are reliable even under unstable network conditions.
* Capable of delivering an offline experience: using service workers and the IndexedDB storage system, PWAs can provide offline experience.
* Safe: PWAs are served over Transport Layer Security (TLS) to ensure a secure connection.
* App badging: PWAs allow badging for app icons to subtly notify users of a new activity that might require their attention [2].
* Capable of supporting custom offline pages and splash screens: like native apps, PWAs support offline pages and splash screens.
* Fresh: PWAs are always kept up to date using the service worker update process.  
* Discoverable: PWAs following W3C manifests are more likely to be discovered by search engines.