Single-Page Application (SPA)

A Single-Page Application (SPA) is a modern web application that loads a single HTML page and then dynamically updates the content as the user interacts with it, offering a fluid, app-like user experience. Instead of performing full page reloads, SPAs use JavaScript to rewrite the current page, a process known as a Soft Navigation. While this can feel smooth to the user, this architecture creates a "measurement blind spot" for many standard performance tools. Core Web Vitals are often only measured for the initial page load, completely missing the performance of subsequent views loaded via soft navigations. This makes it difficult to diagnose performance issues that occur deep within a user's session.