function invert(string) {
let chars = string.split('')
let inverted = chars.map(char => {
if (char.match(/[a-z]/gi)) {
let lowercase = char.toLowerCase();
let index = letters.indexOf(lowercase)
let r = reversed[index]
if (char !== lowercase) r = r.toUpperCase()
return r
} else {
return char
}
})
return inverted.join('')
}