Discussion on: How I improved my code by returning early, returning often!

func main() {
   data, err := loadData()
   result, err := someCalculation(data)
   return result, err
}

Now that code will work fine

No it won't? If loadData() fails, you will then discard that error by calling someCalculations and returning the wrong error to the caller. This code is objectively broken.

const validateAuthorisedPage = (page, isUserAuthenticated) => {
  const authenticatedPages = ['profile']
  if (authenticatedPages.includes(page) && isUserAuthenticated) {
    return page
  }
  return 'login'
}

Those two returns are on mutually exclusive separate branches, yet they're on different indentation levels. Neither of them is a guard clause. In conclusion, this code should be written like this instead:

function validateAuthorisedPage(page, isUserAuthenticated) {
   const authenticatedPages = ['profile']
   if (authenticatedPages.includes(page) && isUserAuthenticated) {
      return page
   } else {
      return 'login'
   }
}

Suddenly it's clear that both returns are on different branches and only one of the two will run every time that code is executed.