Definition
JavaScript rendering is at the heart of modern SEO challenges. There are two main approaches: Client-Side Rendering (CSR), where the browser downloads a minimal HTML shell then executes JS to display content, and Server-Side Rendering (SSR), where the server generates the complete HTML before sending it. Google uses a two-phase rendering system: first indexing raw HTML, then rendering JavaScript in a separate queue (Web Rendering Service). This delay can range from a few seconds to several days. Sites that rely on CSR for their main content risk indexation delays and partially indexed content. SSR, pre-rendering, or hybrid rendering (ISR) are the recommended solutions.
Key Points
- CSR can cause indexation delays of several days
- SSR ensures content is immediately available for bots
- Google uses a Web Rendering Service (WRS) based on Chrome to execute JS
Practical Examples
Problematic CSR
A pure CSR React site finds that Google only indexes the empty HTML shell. Main content, loaded via API calls after page load, doesn't appear in SERPs for weeks.
Migration to SSR
After migrating from CSR to SSR with Next.js, a site sees its pages indexed in less than 24h instead of 2 weeks, with indexation coverage going from 60% to 98%.
Frequently Asked Questions
Google uses a recent version of Chrome (evergreen Chromium) for JS rendering. It can execute most modern JavaScript, but with limitations: rendering timeout, no simulated user interaction, and a queuing delay before rendering.
CSR is not ideal for main content SEO. However, it is acceptable for non-essential elements (widgets, comments). The best approach is hybrid rendering: SSR for main content, CSR for interactive elements.
Go Further with LemmiLink
Discover how LemmiLink can help you put these SEO concepts into practice.
Last updated: 2026-02-07