example.js

// Version 1.0.0

function changeCase (theString) {
  return theString.toUpperCase()
}

// Version 1.1.0 (Feature)

function changeCase (theString, allowLowerCasing = false) {
  if (allowLowerCasing && theString.toUpperCase() === theString) {
    return theString.toLowerCase()
  }
  return theString.toUpperCase()
}

// Version 2.0.0 (Breaking)

function changeCase (theString, allowLowerCasing = false) {
  if (theString.match(/\d+/g)) {
      return new Error('No Numbers allowed!')
  }
  if (allowLowerCasing && theString.toUpperCase() === theString) {
    return theString.toLowerCase()
  }
  return theString.toUpperCase()
}