How do I find JavaScript errors on my website?

Updated 2026-10-17

Short answer: a single script error can stop a button, a menu or a form working while the page itself loads normally. Requests the browser blocks under CORS do the same to anything that calls another service. You only see them in a real browser's console.

How to check it yourself

  1. Open the page, then developer tools, then Console.
  2. Reload and look for red errors and messages mentioning CORS.
  3. Repeat on your contact, checkout and other important pages.
  4. Click the file and line next to each error to see where it comes from.

Why it matters

JavaScript runs menus, forms, carts, sliders and tracking on most sites. When it throws an error, the page usually still loads, but the feature it powers silently stops working. Visitors rarely report it; they just leave, so these errors can go unnoticed for a long time.

Common causes

  • A plugin, theme or app update changed a script.
  • Two scripts conflict, often two copies of the same library.
  • A script loads from another service that's down or has changed.
  • The browser blocks a request under CORS or a Content Security Policy.

What Preventionlabs shows

Every report opens your homepage and up to 3 more pages from your sitemap in a real Chrome browser, as a visitor would, and reports uncaught JavaScript errors and requests the browser blocks under CORS. Nothing is clicked, typed or submitted.

Errors that only happen after clicking or typing need the console steps above.

Price

First report free, no card needed. Then A$50 a month, up to 10 domains.

Run your first report free

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