text: const numberRegex = /\d+/g
  const nonLetterRegex = /\W+|_/gi
  
  module.exports = str => {
    if (typeof str !== 'string' || numberRegex.test(str) || !str.length || !str)
      return 0
    const result = str
      .replace(nonLetterRegex, '')
      .split('')
      .reduce((acc, char) => {
        acc[char] ? acc[char]++ : (acc[char] = 1)
        return acc
      }, {})
    return Object.keys(result).filter(key => result[key] === 1)[0]
  }
  