Excel Sheet Column Number

/**
 * @param {string} s
 * @return {number}
 */
var titleToNumber = function(s) {
    var m = ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ‘.split(‘‘);
    var d = {};
    m.forEach(function(w, i){
        d[w] = i + 1;
    });
    // console.log(d);
    var len = s.length;
    var ret = 0;
    var pow = 1;
    for (var i = len - 1; i >= 0; --i) {
        ret += d[s[i]] * pow;
        pow *= 26;
    }
    return ret;
};