Excel Sheet Column Title

Given a positive integer, return its corresponding column title as appear in an Excel sheet.
For example:

1 -> A
2 -> B
3 -> C
...
26 -> Z
27 -> AA
28 -> AB 

var convertToTitle = function(n) {
    var ans = '';
    var a = 'A'.charCodeAt();
    while(n > 0) {
        n -- ;
        ans= String.fromCharCode(a + n % 26) + ans;
        n = parseInt(n / 26)
    }
    return ans;    
};