Traditional website monitoring assumes pages reload completely when users navigate – but SPAs break this fundamental assumption. Single-page apps use JavaScript to change pages dynamically, without reloading the root HTML page, creating what's known as "soft navigation" versus traditional "hard navigation."
This fundamental difference means traditional performance metrics like Page Load Time (PLT) and Core Web Vitals are quite inadequate as they are only computed when a full page refresh occurs. Most monitoring tools designed for traditional websites will completely miss the majority of user interactions in your SPA.
A SPA hard navigation is the first navigation to the site, plus any of the work required to build the initial view, whilst a SPA soft navigation is any navigation after the first hard navigation where the view changes, but the browser does not actually fully navigate.
Your monitoring solution must handle both types distinctly. Hard navigation metrics remain important for initial load performance, but soft navigation monitoring becomes crucial for understanding the ongoing user experience.
SPAs rely heavily on API calls to load data for pages, making API monitoring essential rather than optional. Unlike traditional websites where data comes pre-loaded in server-rendered pages, SPAs fetch data dynamically through XMLHttpRequest (XHR) and Fetch API calls.
When XHR instrumentation is enabled, monitoring tools will track XMLHttpRequest requests, Fetch API requests, and mouse clicks for non SPA sites. Modern monitoring platforms can track trends for high-value XHR calls, for example, those made to add a product to a cart.
Key metrics to monitor include:
One of the main challenges of monitoring SPA performance resides in the fact that this is difficult to link a specific user action to related JavaScripts execution and API calls. Users click buttons, navigate routes, or submit forms – but determining which subsequent API calls relate to those actions requires sophisticated tracking.
Vue.js applications using Vue Router present specific monitoring challenges. Client-side routing is used by single-page applications (SPAs) to tie the browser URL to the content seen by the user, but traditional monitoring tools often can't track these route changes as distinct page views.
SPAs can emulate multi-page applications with virtual pages, creating the perception of a new page when a user navigates through your SPA, the URL in the address bar changes, but the page doesn't actually reload. Your monitoring must track these virtual page views to understand user journeys.
For Vue Router applications, monitor:
Managing the browser's history and enabling back and forward navigation while maintaining the application's state is crucial for a smooth user experience. Route changes can trigger multiple API calls, component mounting, and data processing – all of which should be measured.
SPAs present several unique challenges that may result in more LoAFs and make them difficult to troubleshoot. The Interaction to Next Paint (INP) metric, whilst useful, tends to ignore the vast majority of interactions that take place in these apps, counting only the worst-performing one on the page.
JavaScript execution can directly impact the user experience if it takes too long to execute and block the main thread of the browser, causing users to experience an unresponsive application. Monitor JavaScript execution time, especially during route transitions and data processing.
Real user monitoring gives you a complete overview of the geographical location of your users and their actual experience while navigating the SPA. RUM becomes particularly valuable for SPAs because synthetic testing tools don't reflect the perceived loading speed of your SPA (which is the only thing that matters to users).
SPAs load the entire application logic in the browser, potentially consuming more memory. Unlike traditional websites where each page starts fresh, SPAs accumulate state and resources over time.
Monitor for:
Errors happen, your single-page app can crash – you need to know this! Don't rely on your users telling you. SPAs introduce unique error scenarios:
Single-page apps can have hard and soft page loads, requiring one additional configuration watcher dedicated to listening for the routeChange event. Ensure your monitoring tool properly detects and reports on route changes as distinct events.
Custom event tracking allows developers to measure specific interactions within the SPA, such as button clicks, form submissions, and dynamic content loading. Define meaningful business metrics beyond traditional page views.
Real user monitoring gives you a complete overview of the geographical location of your users. API response times can vary significantly by region, affecting the user experience differently across your global audience.
Track not just JavaScript errors, but also:
As SPAs become increasingly sophisticated, monitoring must evolve beyond basic uptime checks. Through Real User Monitoring (RUM) tools that track custom events, performance metrics, and errors, developers gain insights into user behavior and application efficiency.
The key is understanding that SPAs require fundamentally different monitoring approaches than traditional websites. Success depends on tracking the dynamic, client-side nature of these applications rather than trying to force them into traditional monitoring paradigms.
With Metrics+, you can be confident that your SPA monitoring captures both the initial load performance and the ongoing user experience throughout their journey. Our Essential and Agency Pro plans provide the comprehensive tracking needed to ensure your single-page applications deliver optimal performance for every user interaction. Subscribe today to start monitoring your SPAs properly.