Optimizing JavaScript Websites for Search Engines

How search engine bots process JavaScript when crawling a web page - Crawling, Rendering, and Indexing.

JavaScript is commonly used to build interactive websites. However, this can cause issues for search engine crawlers trying to index the content. In this post, we’ll go over how crawlers process JavaScript, problems that can occur, and best practices to ensure your JS site gets properly indexed.

How Crawler Bots Process JavaScript

Here are the key phases of how Google processes JavaScript when crawling pages:

  • Crawling – The bot downloads the HTML code and identifies JS resources needed to render the page.
  • Rendering – A headless browser executes the JS code to fully render the content.
  • Indexing – The rendered page is processed and added to the search index.

The bot queues up pages for rendering based on available computing resources. So if your JavaScript takes a long time to execute, it may not get indexed properly.

Server-Side vs Client-Side Rendering

There are two main ways JS can be implemented:

  • Server-Side Rendering (SSR) – JS executes on the server and returns rendered HTML. This is faster and easier to crawl.
  • Client-Side Rendering (CSR) – JS executes in the browser to render content. Initial HTML is minimal. Provides more interactivity but can hinder crawling.

Generally, SSR is better for SEO while CSR allows more complex web apps. A hybrid approach is common.

Tips for JS SEO

Here are some tips to help bots properly crawl and index your JavaScript site:

  • Check for rendering errors using site inspection tools.
  • Don’t block critical JS resources in robots.txt.
  • Minimize page load times as much as possible.
  • Use internal links to help bots discover content.
  • Prioritize loading content over images when lazy loading.
  • Use static URLs instead of hash URLs.
  • Consider SSR for important pages.

Regularly Audit Your Site

Run regular audits using site crawling tools to catch any JS SEO issues. By following best practices, you can build fast, interactive websites that also get properly indexed and ranked.