old_contents: const isString = require(`./isString`)
  const compact = require(`./compact`)
  
  module.exports = function transformClassName (className) {
    if (isString(className)) {
      return className
    } else if (Array.isArray(className)) {
      return compact(className).join(' ')
    }
  }
  
new_contents: const isString = require(`./isString`)
  const compact = require(`./compact`)
  
  module.exports = function transformClassName (className) {
    if (isString(className)) {
      return className
    } else if (Array.isArray(className)) {
      return compact(className).join(` `)
    }
  }
  
subject: Use backticks onstead of quotes