Contains Javascript errors
This means that the URL in question contains JavaScript errors.
Why is this important?
JavaScript code may contain syntax errors or logical errors, which can sometimes lead to big issues when rendering the HTML.
As Tomasz Rudzki from Onely notes, "a single error in your JavaScript code can cause Google to be unable to render your page", and quotes:
He goes on to quote an example of a site that had a JavaScript error which caused pages to drop out of the Google index - only returning once they have fixed the JavaScript error.
SoJavaScript errors can cause rendering issues for users, and potentially have a negative effect on your SEO.
What does the Hint check?
This Hint will trigger for any internal HTML URL that contains JavaScript errors. If you open Chrome DevTools you can see JavaScript errors logged in the console:
How do you resolve this issue?
You're going to need to spend some time debugging the code through your go-to browser, so you can understand what is throwing the error, before you can fix it. If you are unfamiliar with debugging JavaScript, see the links below.