Helper function to create Excel-column-like alphabet sorting values; e.g. 1 --> A, 2 --> B, 27 --> AA, 28 --> AB, etc

excel-column-sort.ts

function numberToLetters(index: number): string {
    const charLimit: number = 26;
    if (index > charLimit) {
        if (index % charLimit === 0) {
            return `${numberToLetters((index / charLimit) - 1)}${numberToLetters(charLimit)}`;
        } else {
            return `${numberToLetters(Math.trunc(index / charLimit))}${numberToLetters(index % charLimit)}`;
        }
    } else {
        const a: number = 'A'.charCodeAt(0);

        return String.fromCharCode(a + index - 1);
    }
}


// Or if needed without TypeScript or ES6 template strings
function numberToLetters(index) {
    var charLimit = 26;
    if (index > charLimit) {
        if (index % charLimit === 0) {
            return '' + numberToLetters((index / charLimit) - 1) + numberToLetters(charLimit);
        } else {
            return '' + numberToLetters(Math.trunc(index / charLimit)) + numberToLetters(index % charLimit);
        }
    } else {
        var a = 'A'.charCodeAt(0);

        return String.fromCharCode(a + index - 1);
    }
}