10. Letters Change Numbers

function lettersChangeNumbers(input) {
    let result = input
        .split(' ')
        .filter(word => word.length)
        .map(word => {
            let firstCharacter = word.substring(0, 1);
            let secondCharaster = word.substring(word.length - 1);
            let number = Number(word.substring(1, word.length - 1));

            if ('A' <= firstCharacter && firstCharacter <= 'Z') {
                number = number / (firstCharacter.charCodeAt() - 64)
            } else {
                number = number * ((firstCharacter.charCodeAt() - 96));
            }
            if ('a' <= secondCharaster && secondCharaster <= 'z') {
                number += (secondCharaster.charCodeAt() - 96)
            } else {
                number -= ((secondCharaster.charCodeAt() - 64));
            }
            return number
        })
        .reduce((a, b) => (a + b), 0)

        console.log(result.toFixed(2));
}