What is a Single Page App and How it Works?

We’ll take a look at what is a single-page app, and take a look at some real-world SPA examples and what frameworks they use.

Single-page applications (SPAs) are a great way to provide a smooth user experience. They load quickly, simplify development, and use less server power.

It’s no surprise that they’re becoming more popular, with big names like Google using SPAs for services like Gmail and Google Maps.

If you’re considering building an app, an SPA could be the right fit if you need something fast, compatible across platforms, and packed with features—whether it’s for a SaaS business, a social network, or another type of application.

But what exactly is an SPA?

In this article, we’ll explain what single-page applications are, list their benefits and drawbacks, and take a look at some real-world examples and what frameworks they use.

By the way, you’ll come across these abbreviations in this article, so we’ll list them here:

• SPA: Single-page application (covered here)
• MPA: Multi-page application (traditional apps that load new pages when you click a link)
• PWA: Progressive web application (websites built with JavaScript that function like mobile apps)

What Is a Single Page Application?

In short, a single page application (SPA) is a web app that loads content dynamically without refreshing the entire page, unlike traditional websites that reload fully every time you click a link.

When you interact with a SPA, the app sends just the necessary data to your browser and updates the current page. In contrast, a traditional site would reload the entire page from the server. The result? Faster interactions and fewer interruptions.

	SPA	MPA
Definition	A web app that loads a single HTML page. New content gets updated dynamically without a full page reload.	A web app with multiple HTML pages. Each navigation or data request reloads the entire page.
Best Use Cases	– Mobile app development – SaaS platforms – Social media sites – Private networks with login requirements – No need for SEO	– SEO-friendly websites – eCommerce platforms – Company websites – Blogs
Code Structure	Frontend and backend code are typically kept separate.	Frontend and backend code often overlap.
Speed	Longer initial load time, but faster and more fluid interactions afterward.	Generally slower navigation; speed depends on page size and internet quality.
Security	More challenging to secure against cyber threats.	Generally easier to protect against security vulnerabilities.
Memory Consumption	Can run for long periods, which may lead to high memory usage.	Reloading pages frequently reduces the risk of memory leaks.

Technically speaking, SPAs rely on your browser to handle most of the work. All the HTML, JavaScript, and CSS needed for the app loads initially or gets added as you use the site. The page doesn’t reload during this process, though some tricks like the HTML5 history API or location hash can make it feel like you’re navigating different pages.

The best case scenarios where you should build your application as SPA include:

• Apps with lots of dynamic interactions where reloading the page would be disruptive.
• When your app needs to display real-time data without a page refresh.
• If you want a web app that feels similar to a mobile app.
• When cutting down on server requests and bandwidth is important.
• For single-page content.
• Apps that need to work the same way across different devices.

How Does it Work?

Think of it like painting a picture. On a traditional website, every time you request something new, the server paints the whole picture again and sends it to your browser. This includes parts that don’t change, like the header, footer, or navigation bar.

In a SPA, the server sends you a paint-by-numbers guide with instructions for the basic layout. If you want to change something, like viewing a different image, the server just sends the new piece of content, and your browser fills in that section. The rest of the picture stays the same.

This works because SPAs handle most of the rendering work in your browser instead of on the server. So, if you click on a new link, filter a list, or open a different section, only the necessary content updates. The server doesn’t need to resend everything, saving time and reducing lag.

This method also takes advantage of repetitive elements, like menus, logos, or banners, which stay consistent across different views. SPAs only update what’s new, making interactions faster and smoother for the user.

There are three main types of rendering used in SPAs, depending on the type of website or app you’re building and how dynamic your content needs to be. In each of these methods, SPAs aim to reduce full-page reloads.

1. Client-side rendering (CSR) for highly interactive apps

This method works well for applications with a lot of interaction and user activity. However, this can backfire for simpler websites, because it relies heavily on the user’s device to do the work.

• The browser requests an HTML file from the server.
• The server responds with a basic HTML file containing links to stylesheets and scripts.
• While JavaScript runs, users might see a blank page or a loading indicator.
• The app fetches data, creates views, and updates the Document Object Model (DOM) accordingly.

2. Server-Side Rendering (SSR) for initial loading

The second method is great for delivering content faster, especially for SPAs that need to balance speed and performance without overloading the user’s browser.

• The browser requests an HTML file from the server.
• The server gathers the required data and builds the complete HTML page on the spot.
• The user immediately sees fully rendered content.
• The SPA then sets up event listeners, generates a virtual DOM, and prepares everything for interaction.

3. Static Site Generation (SSG) for fixed content

The last method is perfect for websites with mostly fixed content, like blogs or documentation sites. They offer quick load times but we don’t recommend this for sites that need to handle constantly changing data.

• The browser requests an HTML file, and the static site generator provides a pre-built static page.
• The server delivers the static page almost instantly for a fast load time.
• The SPA fetches any necessary data and updates the content dynamically.
• The page is ready for interaction once the dynamic content has loaded.

Web Frameworks for SPA Development

When it comes to developing SPAs, there are three frameworks to go to: React, Vue, and Angular. React is great for working on projects with lots of moving parts; Vue for simplicity and flexibility; and Angular for large teams and complex apps, especially in enterprise environments.

ReactJS

React is highly versatile and integrates well with other technologies and frameworks, which makes it a solid choice for large-scale projects. This framework is the backbone for apps like Facebook, WhatsApp, Instagram, and Uber.

It has an enormous community of developers, which keeps it updated and helps tackle any issues quickly. This library is especially great for those new to JavaScript frameworks and for startups or developers who need flexibility in their work.

VueJS

Vue is lightweight, flexible, and easy to integrate. It’s the most lightweight option of the three which makes it an excellent choice for developers who want a simpler, more straightforward framework without sacrificing power.

This framework was created in 2014 by former Google engineer Evan You and is the choice of Baidu, GitLab, and Alibaba for their web applications.

AngularJS

Angular is the oldest of the three frameworks and uses TypeScript for some extra structure which makes it particularly useful for large development teams. It’s also the go-to option for companies that have already integrated TypeScript into their other products.

Google uses AngularJS for several of its applications, including Gmail and Google Drive, and it’s commonly chosen for enterprise-level projects. It’s a mature framework with strong community support and many contributors on GitHub.

Single Page App Examples

Many popular platforms use this architecture to power features we use daily. Gmail, Netflix, Facebook, and others are great examples of how SPAs combine modern front-end frameworks with powerful back-end technologies, so let’s take a closer look at how these platforms are built and what makes their SPAs tick.

1. Gmail

Gmail is a great example of how SPAs work in practice. Users can move between their inboxes, compose emails, and adjust settings without waiting for full-page reloads.

• Front End: Gmail relies heavily on JavaScript for interactive features and uses Angular, a Google framework, to power the application.
• Backend: The backend is built using a combination of C++, Python, and Java to handle email data at scale.

2. Facebook

Facebook uses SPA principles to give users a steady experience while scrolling through their news feed, reacting to posts, or checking notifications.

• Front End: The platform runs on React, a framework developed in-house by Facebook, which drives its dynamic features.
• Backend: A mix of C++, Java, Python, and Erlang powers the backend to handle billions of daily interactions.

3. Netflix

Netflix uses SPA architecture to make browsing its catalog and streaming movies feel quick and effortless.

• Front End: ReactJS handles the interactive interface, while Node.js adds server-side support for faster loading.
• Backend: Spring Boot powers the backend, helping Netflix manage a huge library of content.

4. Pinterest

Pinterest lets users pin ideas, browse boards, and explore content with minimal delay or interruptions.

• Front End: The platform uses React to keep the interface visually appealing and interactive.
• Backend: Built on Python with the Django Framework, the backend also incorporates Java, Objective-C, and Golang for handling complex data workflows.

Pros and Cons of Single-Page Apps

Benefits

Single-page applications load most of their resources, such as HTML, JavaScript, and CSS, at the start. Once loaded, these don’t need to be fetched again during use. The only updates happen through data transfers, which keeps the app quick and responsive.

👍 Faster Load Times 

SPAs load all necessary resources—HTML, CSS, and JavaScript—during the first visit. Once the initial setup is complete, only small data packets are exchanged with the server. This reduces waiting time for users and keeps the browsing experience quick.

👍 Reduced Server Workload

The strain on servers decreases because SPAs don’t require full-page reloads. Data-only communication lightens the load, allowing businesses to manage higher traffic without additional infrastructure.

👍 Independent Development Processes

Developers can separate front-end and back-end tasks, so they can work on each independently without causing conflicts. This also allows for component reuse, which saves time while maintaining consistency across projects.

👍 Better User Interaction

SPAs provide a fluid browsing experience because they update content dynamically without interrupting navigation. Users will be able to enjoy uninterrupted scrolling and quick transitions, especially on mobile devices.

👍 Offline Accessibility

SPAs store data locally after the first interaction with the server. Thanks to that, users can interact with the application even without an internet connection. Any updates made offline will sync automatically once the connection is restored.

👍 Debugging Made Simpler

Modern SPA frameworks, like React and Angular, include developer tools that simplify troubleshooting. This includes features such as network monitoring and code inspection that make identifying and resolving issues much faster.

👍 Works Across Devices

SPAs adapt to various devices, operating systems, and browsers with a single codebase.

👍 Lower Bandwidth Consumption

Since SPAs reload only parts of the page, they use less bandwidth. This is perfect for users with slower connections or limited data plans. Local caching further reduces data usage, which improves accessibility for users in remote locations.

Drawbacks

Developers also face some trade-offs when deciding to use an SPA. There are workarounds for many of the issues listed, but those require careful planning and added effort during development.

👎 Limited Browser History

SPAs don’t naturally save a record of your actions within the app. If you click the back button it will often take you to the last page you visited, instead of the previous state within the application. Developers can address this issue with tools like the HTML5 History API, but it requires extra effort and careful implementation.

👎 SEO Challenges

SPAs struggle with search engine optimization because they rely on JavaScript and single URLs. Search bots have difficulty indexing content because pages often don’t have unique URLs or metadata. Google has made some progress in indexing JavaScript-based websites, but developers still need to fine-tune their code to make it crawlable.

👎 Vulnerability to Security Risks

SPAs are more prone to certain online threats, especially cross-site scripting (XSS) attacks. Hackers can exploit client-side scripts to access sensitive information or compromise functionality. Additionally, because much of the app’s logic and features are moved from the server to the client, it’s easier for attackers to uncover vulnerabilities. Developers must take extra precautions to protect sensitive data and control access at every level.

👎 Slower Initial Load Times

Loading an SPA for the first time requires downloading all the necessary code and resources. This can lead to noticeably longer load times, especially for users with slower connections. Of course, SPAs perform fast after this initial setup.

👎 Navigation Limitations

SPAs don’t store browser history in a detailed way, which means users can’t rely on the back and forward buttons as they would with traditional multi-page apps.

Final Words: When to Use SPAs

SPAs have both advantages and challenges, so there isn’t a clear-cut answer about whether they’re always the best choice. It really depends on your project’s needs and objectives.

If you’re building a website with lighter data requirements and a lot of dynamic content, SPAs could be a good fit. They’re also useful if you’re planning to expand into mobile apps later, as you can use the same backend API for both your website and app.

SPAs work well for platforms like social networks, private communities, or SaaS applications, especially when SEO isn’t a top priority. If your goal is to offer a smooth user experience with minimal delays, an SPA is worth considering. Apps like Google Maps, for instance, use SPAs to update information in real-time as users navigate.

They’re also ideal if you need features like live updates, real-time charts, or notifications. If providing a consistent and interactive user experience across various devices and browsers is important, SPAs can help you achieve that.

If you’re thinking about starting an SPA project, we’d love to help. Reach out to us to chat about your ideas and how we can build the best SPA for you.

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