So, I read the article: "How to Handle API Errors"

In this article, it is proposed to divide errors into:

if (err.response) { 
      // client received an error response (5xx, 4xx)
    } else if (err.request) { 
      // client never received a response, or request never left 
    } else { 
      // anything else 
    } 

Ok, but how i can test this?

• Response errors are pretty easy. I use Mokku chrome extension.
• Else errors i can simulate with chrome dev tools 'network request blocking' tab.

But what about request Errors? How can i simulate this error on frontend?