How can I understand what this error in reactjs is?

You have a User Script installed in your Chrome browser, which I'm guessing is unrelated to your project. When the current URL matches a certain pattern, this particular script runs, checks for a cookie being set and then stops the remainder of the script from running by throwing an error.

To be honest, that script looks like it could potentially be malicious if you don't know what it is and it is not part of your project. If I had something like this, I'd be looking at what those URLs relate to and disabling the userscript if they look suspicious.