Clone the repo.
npm install
npm run build --> webpack ./hello.js hello.bundle.js
You get: ERROR in multi ./hello.js hello.bundle.js Module not found: Error: Can't resolve 'hello.bundle.js'
Now, when you do:
webpack ./hello.js -o hello.bundle.js
This will generate a hello.bundle.js.
Now when you execute:
webpack ./hello.js hello.bundle.js (again as the first time without -o flag)
It will work. But it will not work if the output bundle does not already exist!