// remove non-letters from a string
function lettersOnly(str) {
    return str.replace(/[^a-zA-Z]/g,"");
   //or return str.match(/[a-z]/gi).join('');
   //or return str.replace(/[^a-z]/gi,""); 
}

console.log(lettersOnly("R!=:~0o0./c&}9k`60=y"));        //"Rocky"
console.log(lettersOnly("^,]%4B|@56a![0{2m>b1&4i4"));    //"Bambi"
console.log(lettersOnly("^U)6$22>8p)."));                //"Up"