Browser errors were logged to the console

Lighthouse flags any browser errors logged to the console:

Lighthouse audit showing browser errors in the console
Fig. 1 — Browser errors logged to the console

How this audit fails

Most browsers ship with built-in developer tools. These developer tools usually include a console. The console gives you information about a page while that page is running. Ultimately, the messages you see in the console either come from the web developers who built the page, or the browser itself.

When someone logs a message to the console, they can indicate the importance, or "severity level" of the message. An "error" message is an important message representing an unresolved failure in the page. In other words, when you see an error, the page isn't running as intended.

An example of console errors in Chrome DevTools
Fig. 2 — An example of console errors in Chrome DevTools

Figure 2 shows two errors. The top one comes from a web developer, via a call to console.error(). The bottom one comes from the browser, which indicates that a variable used in one of the page's scripts does not exist. Lighthouse flags the browser errors.

Each Best Practices audit is weighted equally in the Lighthouse Best Practices Score. Learn more in The Best Practices score.

How to fix the browser errors

Fix each of the errors that Lighthouse reports to ensure that your page runs as expected for all of your users. If the cause of the error is not clear to you, copy the error text and paste it into a search engine. If you can't find solutions to your problem, try asking a question on Stack Overflow.

Chrome DevTools can help you track down the cause of the errors. Take the top error in Figure 2 for example. Clicking the pen.js:9 link in the top-right of that error shows you the code that caused that error. Below the text this is an example of a console error..., there is the call stack that caused the problematic code to execute.

The bottom function (anonymous) called the init function, which called the doStuff function. Open the Chrome DevTools Console by pressing Command+Option+J (Mac) or Control+Shift+J (Windows, Linux). See Using The Console to learn more.

If you can't fix the errors, at least consider wrapping them in try...catch statements to explicitly indicate in the code that you're aware of the issue. You can also use the catch block to handle the error situation more gracefully.

More information

Browser errors logged to console audit source

Last updated: Improve article