npm WARN enoent ENOENT: no such file or directory, open 'C:\Users\Nuwanst\package.json'

Have you created a package.json file? Maybe run this command first again.

C:\Users\Nuwanst\Documents\NodeJS\3.chat>npm init

It creates a package.json file in your folder.

Then run,

C:\Users\Nuwanst\Documents\NodeJS\3.chat>npm install socket.io --save

The --save ensures your module is saved as a dependency in your package.json file.

Let me know if this works.

If you already have package-lock.json file just delete it and try again.

Delete package-lock.json it works for me

then npm install