Progressive Web Apps

Progressive Web Apps (PWA) are app-like web pages that can be opened on mobile devices via a browser.

These cross-breeds of traditional websites and mobile apps can be indexed by Google just like any regular website. At the same time, content can be used in the same way as with a native app, and be made available across platforms. In the future, PWAs are likely to play an important role in mobile optimization. PWAs can be traced back to an initiative supported by Google.

What are Progressive Web Apps?

Progressive Web Apps (PWA) are app-like web pages that can be opened on mobile devices via a browser. Progressive Web Apps have all the advantages of native apps, without having to be installed on the user’s device. Furthermore, Progressive Web Apps are easier to create, crawl and visit.

Why use Progressive Web Apps?

There are several ways for webmasters to make their content available to users on mobile devices. One way is to optimize their website for mobile devices by implementing responsive design. If this option is chosen, all content can be viewed on almost any device, because the website will adjust to the display size and the functions of the device it is being loaded on. Other webmasters prefer to use native apps. These are separate programs (applications), that are installable from an application library (App Store on iOS, Play Store on Android, Microsoft Store on Windows) on a tablet or smartphone. These native apps are not offline programs – they do display content from the web, but they are closed systems that usually lack any direct link to search engines.

In recent years, Google has reacted to the move towards closed web systems by taking steps like enabling app-indexing . This makes it possible to create links to the URLs within an app and have these indexed by Google. If a user now searches on Google, results from apps can be displayed, provided the apps are already installed on their device. The download page of an app in the app store can also be provided as a mobile search result.

Google supported the initiative of Progressive Web Apps with the aim of opening up access to as much web content as possible, especially in terms of crawlability for search engine robots. This blend of apps and websites is part of Google’s principle of Progressive Enhancement, which means that websites should not have to provide different functionalities for different user devices, but should be responsive, always adapting to the appropriate client. One element of this is that Progressive Web Apps should always take into account the specificities of mobile web usage, without requiring the installation of a separate application.

Progressive Web Apps should make it possible for users to:

• Access content on any device
• Access web content even when the internet connection is weak or not available
• Load websites quickly
• Benefit from a high-quality user experience

Google defines the most important characteristics of Progressive Web Apps as follows:

• PWAs are reliable because they load content even when the connection is weak or insufficient for normal internet usage.
• PWAs are also very fast because they react immediately to user input. This almost completely eliminates delays when loading a site or scrolling.
• Finally, PWAs provide an optimized user experience that replicates that of native apps.

How do Progressive Web Apps work?

The foundation that Progressive Web Apps are built on is “service workers”. These are JavaScript files that make it possible to load cached content in the background. This JavaScript works offline, and does not require an internet connection. Another advantage of service workers is that delays when calling up another page are almost completely eliminated.

The scope of the service workers goes even further. When a Progressive Web App is in development, the service workers’ tasks are defined and stored as a script. This makes it possible to configure complete programmatic processes that depend on particular events and trigger pre-defined actions. In this way, a PWA can be created to load content even before a link has been clicked on.

For a Progressive Web App to work in any browser, it requires the so-called application shell. This ensures that a mobile view of the URL is generated, and that the app is adapted to the functionality of the browser being used. The application shell is also responsible for the design of the PWA reflecting the look of a native app. This means that the app shell is the basis of dynamically loading content. It is loaded into the device’s cache when the PWA is called.

The third important component of a PWA is the web app manifest. This is a JSON file that is saved on the server. This manifest file enables the user to save the PWA, once it has been called, on their device like a native app. In fact, it is not the whole application that is installed, as would be the case with a native app, but just the foundation in the form of (at least) an app shell. With the web app manifest, an icon for saving the PWA can be placed on the home screen. It also makes it possible to define whether the app can be loaded without a browser or in an available browser. The script could also be used to manage the look and/or functions of the app. Finally, it is possible to enable push notifications to be sent to users, providing the users agree to this capability when “installing” the app.

What are the advantages of Progressive Web Apps?

Progressive Web Apps offer webmasters numerous advantages:

• It is much more cost-effective to develop a PWA than a native app.
• Maintaining a PWA does not require much effort.
• PWAs can be kept continuously up-to-date.
• There is no dependency on app stores. Webmasters can promote their PWAs themselves.
• The contents of a Progressive Web App can be indexed and can therefore rank with search engines.
• There are no platform limitations. This means that users can view the contents of a PWA on any mobile device.
• Web content can be accessed over almost any quality of connection.
• The connection between the user and the web content is strengthened by the “installation” of the PWA.

Why does Google like Progressive Web Apps?

It is not surprising that Google promotes the use and uptake of Progressive Web Apps, because the majority of mobile internet usage takes place over smartphone apps. This means that search engines like Google only have limited access to user data and, more importantly, that the apps’ contents cannot be fully crawled. With Progressive Web Apps, Google and other search engines have the possibility of gathering data on user behavior even when they are using apps. At the same time, it is possible that PWAs can also be used to display Google advertisements. PWAs would therefore represent an additional market for Google to generate revenue.