RamdaClassNames.js

const classNamesBy = mapper => R.compose(
  R.trim,
  R.join(' '),
  R.chain(mapper),
  R.toPairs,
)

const classNames = R.curry((base, obj) => {
  const standard = ([k, v]) => [v ? k : '']
  const reversed = R.compose(standard, R.reverse)
  
  const baseResult = typeof base === 'string'
    ? base
    : classNamesBy(reversed)(base)
  
  return R.compose(
    classes => `${baseResult} ${classes}`,
    classNamesBy(standard),
  )(obj)
})