Chrome Update Boosts Web Vitals for JS-Heavy Sites
▼ Summary
– Google Chrome is testing a Soft Navigations API in Chrome 139 to measure Core Web Vitals in Single Page Applications (SPAs), addressing a blind spot in performance tracking.
– SPAs often update content without full page reloads, making them difficult to monitor with traditional tools like Lighthouse or CrUX.
– The API detects soft navigations by tracking user clicks, URL updates, and DOM changes, then treats them as navigation events for performance measurement.
– Developers can test the feature in Chrome 139 using local flags or an origin trial, with optional flags like “Advanced Paint Attribution” for more complete data.
– The API is experimental and may not support older browsers or edge cases, but it aims to improve Core Web Vitals accuracy for modern JavaScript-heavy websites.
Google Chrome’s latest update introduces a groundbreaking way to track Core Web Vitals for JavaScript-heavy websites, addressing a critical gap in performance measurement for Single Page Applications (SPAs). This development could significantly impact how developers and SEO professionals optimize modern web experiences.
With Chrome 139, an experimental Soft Navigations API enters origin trials, allowing sites to measure key metrics like Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Interaction to Next Paint (INP) even during dynamic content updates without full page reloads. For SPAs built with frameworks like React or Angular, this solves a persistent challenge where traditional tools often miss crucial user interactions.
The innovation matters because SPAs frequently update content through JavaScript without triggering standard navigation events. Until now, this behavior created blind spots in performance monitoring, making it difficult to assess real-world user experience accurately. Tools like Lighthouse and CrUX reports couldn’t properly capture these interactions, potentially skewing SEO audits and ranking signals.
Chrome’s solution uses intelligent detection to identify soft navigations, instances where users click links, URLs update, and visible DOM changes occur. When these conditions are met, the browser treats them as measurable navigation events.
The API introduces specialized metrics such as interaction-contentful-paint for tracking LCP after dynamic updates. Developers can experiment with two approaches:
- Local testing by enabling Chrome’s `soft-navigation-heuristics` flag
- Production deployment via origin trial tokens for real-user data collection
Barry Pollard, Chrome’s technical lead for the project, encourages early adoption: “Test this on your SPA to verify detection accuracy, your feedback will shape the final implementation.
Important considerations include:
- Browser compatibility limitations outside Chrome 139+
- Potential gaps with automatic redirects or `replaceState()` operations
- The need for RUM providers to adopt new metric tracking
While not yet reflected in public CrUX reports, successful trials could lead to broader integration. For teams managing SPAs, this represents an opportunity to refine performance strategies with data that finally matches how users actually experience modern web apps.
(Source: Search Engine Journal)
