appscriptUtil.js

// check if we are inside GAS
// source - https://github.com/WildH0g/UnitTestingApp/blob/master/UnitTestingApp.js
function inGas() {
  return typeof ScriptApp !== 'undefined';
}

// get the sheet ID from a url
// source - https://stackoverflow.com/questions/16840038/easiest-way-to-get-file-id-from-url-on-google-apps-script
function getIdFromUrl(url) { 
    try {
        return url.match(/[-\w]{25,}/)[0];
    } catch (error) {
        return null
    } 
}

// get the next alphabet to use in a sheet
// source - https://stackoverflow.com/questions/32157500/increment-alphabet-characters-to-next-character-using-javascript
function nextAlphabetString(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
}