How to get the next letter of the alphabet in Javascript?

Question

I am build an autocomplete that searches off of a CouchDB View.

I need to be able to take the final character of the input string, and replace the last character wit

Answer 1

Here is a function that does the same thing (except for upper case only, but that's easy to change) but uses slice only once and is iterative rather than recursive. In a quick benchmark, it's about 4 times faster (which is only relevant if you make really heavy use of it!).

function nextString(str) {
    if (! str)
        return 'A'  // return 'A' if str is empty or null

    let tail = ''
    let i = str.length -1
    let char = str[i]
    // find the index of the first character from the right that is not a 'Z'
    while (char === 'Z' && i > 0) {
        i--
        char = str[i]
        tail = 'A' + tail   // tail contains a string of 'A'
    }
    if (char === 'Z')   // the string was made only of 'Z'
        return 'AA' + tail
    // increment the character that was not a 'Z'
    return str.slice(0, i) + String.fromCharCode(char.charCodeAt(0) + 1) + tail

}