SEO glossary · J

JavaScript

What is JavaScript?

JavaScript is the programming language of the web. It runs in the browser and makes pages interactive: menus, forms that check your input, sliders, maps, calculators and content that updates without reloading the page. With HTML (structure) and CSS (design), it is one of the three core web technologies.

What JavaScript is used for

  • Interactive elements and animations
  • Web apps built with frameworks such as React, Vue, Angular and Svelte
  • Analytics, advertising and tracking codes
  • Server-side code, with Node.js

JavaScript and SEO

Google can run JavaScript and index the content it creates, but that happens in a separate rendering step that can be delayed, and other search engines and AI crawlers may not run JavaScript at all. To be safe:

  • Put important content and links in the HTML the server sends, using server-side rendering or static generation where possible.
  • Use real links (<a href>) rather than click handlers for navigation.
  • Don’t block JavaScript files in robots.txt.
  • Check pages with the URL Inspection tool in Google Search Console.

JavaScript and speed

Heavy JavaScript slows pages down and hurts Interaction to Next Paint. Remove unused scripts, and load third-party tags with care.

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