React.js "Yarn start" is running, but can't open the app in the browser-CodePudding

I have a React application. I have installed the packages with yarn and ran it with yarn start. But, the app is not opening in the browser. The console shows me the following:

Compiled successfully!

You can now view extension in the browser.       

  http://localhost:3000

Note that the development build is not optimized.
To create a production build, use yarn build.    

webpack compiled successfully
Files successfully emitted, waiting for typecheck results...
Issues checking in progress...
No issues found.

But when I open the browser at localhost:3000 and it shows nothing, but:

This site can’t be reached
localhost refused to connect.

Did anyone have this kind of issue? Any kind of help would be appreciated.

PS: I tried to remove node_modules and install packages again, npx clear-npx-cache as well, but nothing worked.

Update After I build the app with yarn build and run serve -s build then I can access the app on localhost:3000. Why this happens?

CodePudding user response：

have you tried with "PORT=3000 react-scripts start" in your "start" script? you could actually try with any other port like "PORT=3001 react-scripts start" and see if that fixes the problem.

CodePudding user response：

If you have used

yarn create react-app my-app

It will look like this.

The package.json will look like