What Are Single-Page Applications and Progressive Web Apps?

Alvaro Abril, Full Stack Developer. Founder SistemasGeniales.com / Dineroclub.net, presidencia@dineroclub.com

If you’re keen to uncover the differences between these two web heavyweights, keep reading.

Single-page applications (SPAs) and Progressive web apps (PWAs) are revolutionizing the web. They’re both novel technologies that look similar, but are not. In face, people often use them interchangeably.

Let’s dig into the core features and architecture of each of them to understand them better.

What Are Single-Page Applications?

SPAs, as they sound, are websites that load content dynamically within a single page. In essence, every form of content and element you need to interact with stretches on one page. That means you don’t need to load separate Document Object Models (DOMs) when navigating such a website.

That said, the aim is to keep users on the same page by loading all they need to use and see at once. This translates to a better user experience.

The user interface, on the other hand, depends on how you design and arrange your SPA. This boils down to why you may want to break the stretched page into navigations. And that doesn’t stop it from being a single page, as content still loads only once.

So, when you navigate on a SPA, you’re browsing preloaded content in a single DOM and not visiting different DOMs as you may have wrongly believed.

Breaking an SPA into separate content sections usually involves giving each of them a URL using JavaScript views. The data-link connector links those sections to the main DOM and allows you to access them asynchronously.

Although other technologies like Mint and elm-spa are coming up, JavaScript is still the most common programming language for crafting SPAs.

JavaScript uses an async/await function that lets you load both dynamic and static content asynchronously without one input blocking the output of another request. So, SPAs operate on a non-blocking input-output (I/O) system.

That said, JavaScript frameworks like ReactJS, Vue.js, AngularJS, Ember.js, and Backbone.js all support the rapid development of SPAs. To get started, you can go through this beginner’s overview of Vue.js.

Because it confers speed, most enterprise apps have adopted the idea of transforming their websites into a single page. Netflix, YouTube, PayPal, Facebook, Instagram, Twitter, and Pinterest are all examples of SPAs.

What Are Progressive Web Apps?

A PWA is a web application or software that uses standard and emerging web browser guidelines in its functionality. PWAs, unlike SPAs, base their architecture on some set of guidelines that makes them scalable, user-adaptable, super-fast, installable, and native-like.

Introduced in 2015 by Google, the goal of a PWA is to build apps that talk directly and progressively to its users. It aims to keep users flowing with the app, even when there’s a poor or non-existent network connection.

Invariably, a PWA delivers all you need in a snap. It doesn’t go through the typical initial content loading characteristic of a SPA.

Consequently, a user then interacts with the app as if it’s native. Although a core characteristic of PWAs is installability, you can still access them on the fly via your web browser without any installation. That said, like any other website, a PWA must also have a URL.

Progressive web apps are unique in that they have background helpers that deliver content within the twinkle of an eye. So, even before getting to the web app, content and components are readily available for you to use. That makes them super-fast and more reliable.

Apps like Spotify, Slack, and Uber, among others, are examples of PWAs.

PWAs generally have a common architectural rule. For a PWA to function the way it should, it must have the following attributes:

1. A Worker

Service workers deliver content readily in PWAs. They ensure that your app can load relatable cached data when there’s no network connection. This is possible with the help of the Cache API, which stores responses to your offline requests. Thus, a worker interferes with navigations and user requests.

Using a promise object, a worker can deliver already downloaded content in case of an eventual request by a user (even when they’re offline). A service worker, however, confers a non-blocking property on PWAs.

2. A Secure Context

A service worker needs a secure connection (HTTPS) for the confidentiality of the delivered content. When you send a request, a worker establishes secure communication between the PWA and the browser. A secure context, therefore, prevents confidentiality breaches like a man-in-the-middle attack (MITM) in PWAs.

3. A Web Application Manifest File

A web manifest is a JSON file that defines the characteristics of a PWA. It details the prerequisites for accessing, discovering, and using the content of a PWA. It usually includes the name of your app, its URL, and its components. Ultimately, a manifest file contains the information necessary to turn your web app into an installable application.

What Are the Similarities Between PWAs and SPAs?

While the background logic of PWAs and SPAs are different, they still share only a few things in common. Although their delivery speed may differ significantly, conventional websites still fall behind them in speed and accessibility.

They both aim to improve the user experience by providing a responsive interface.

Because they both deliver an app experience, it’s easy to mix them up, and you can hardly tell which is which when you interact with them. Finally, on this note, both need a URL before you can access them.

The Key Differences Between SPAs and PWAs

PWAs and SPAs may share some noticeable characteristics in common, but they’re two different things. Here are the key feature differences you should note:

Key Features of Single-Page Applications

  • They’re only accessible through the browser.
  • Although not recommended, you can serve them over an insecure network (HTTP).
  • They don’t require service workers.
  • SPAs don’t have a JSON manifest file, which means they’re uninstallable.
  • They must be single-page.
  • Not accessible when there’s no network.

Key Features of Progressive Web Apps

  • Accessing them through the browser is an option since they’re installable.
  • All PWAs need service workers and they must make requests through a secure network (HTTPS).
  • Responses are cached and delivered through a promise object.
  • They’re accessible even in the absence of a network connection.
  • They’re faster than SPAs.
  • They always have a manifest file, so they’re downloadable, installable, and readily accessible.
  • A PWA may not be a single-page application.

SPAs and PWAs Are Influencing Website Delivery

With many enterprise websites now adopting these new technologies, there’s now a positive shift towards their service delivery.

More importantly, the adoption of PWAs improves general user experience, which consequently reduces bounce rates and increases revenue for most enterprise apps. SPAs, on the other hand, have also rejuvenated social media, making it easy for people to interact over the web without sluggish page loads.

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