How to Find JavaScript Errors That Are Hurting Your Website

Invisible errors

Most JavaScript errors in production are silent. They don't show a dialog to the user. They don't appear in your analytics. They surface in the browser console — which your users never open. By the time someone notices, the error may have been present for weeks.

Types of runtime errors

The most common runtime errors are TypeErrors — typically trying to access a property on undefined or null. These often indicate that an API returned unexpected data or that a component rendered before its data was available.

• TypeError — property access on undefined/null
• ReferenceError — variable not defined in scope
• SyntaxError — invalid code that passed linting but failed at runtime
• NetworkError — fetch or XHR request failed

Failed network requests

Failed requests are often overlooked because they don't throw visible errors. A 404 on a JavaScript bundle, a failing API call or a missing third-party resource can degrade functionality without producing an obvious error message.

How to find them

An automated audit visits your page in a real browser context and captures all console errors, warnings and network failures. This gives you a complete list of runtime issues without requiring manual inspection across every page.

The key information you need for each error: the error message, the source file and line number, and the page URL where it occurred.

Fixing by priority

Fix errors on high-traffic and high-conversion pages first. A checkout page with a TypeError is more urgent than a rarely-visited blog post with a missing resource. Prioritize by page importance, not by error type.