Unity communicates with Node.js through socket.io, but the server does not respond to the callback of successful connection from the client

I was looking at the communication solution on the Internet. At that time, I operated the server to turn it on. After the client was turned on, the server did not respond to the callback of the successful connection of the client. I found a lot of solutions, and even tried the Unity version to 2017, but it still didn't respond. . . Record the solution I found, so that everyone can avoid related problems.

Solution:

• Delete the package originally downloaded through npm install socket.io and use npm install socket.io@^2.1.1 to download it.