excel sheet index conversion

gistfile1.txt

// minified
a=>a.toUpperCase().split('').reduce((b,c)=>b*26+c.charCodeAt(0)-"A".charCodeAt(0)-1,0)

// one-lined
column => column.toUpperCase().split('').reduce((acc,val) => acc * 26 + val.charCodeAt(0) - "A".charCodeAt(0) - 1,0);

// expanded
function convert_column_to_index(column_name) {
    return column_name.split('').reduce(function(acc,val) {
        return acc * 26 + val.charCodeAt(0) - ("A".charCodeAt(0) - 1)
    }, 0);
}

// william 

function nameToIndex(input) {
    var indexNum = 0;
    var inputArray = input.split("");
  
  inputArray.reverse();

    for (var i = 0; i < inputArray.length; i++) {
      indexNum += (Math.pow(26, i) * (inputArray[0].toLowerCase().charCodeAt() - 96));
  }

    return indexNum;
}

// alt
function convert_column_to_index(column_name) {
    return column_name.split('').reduce(function(acc,val) {
        return acc * 26 + ("abcdefghijklmnopqrstuvwxyz".indexOf(val) + 1)
    }, 0);
}

//tests
expect("a").toBe(1);
expect("z").toBe(26);
expect("aa").toBe(27)'
expect("bb").toBe(54)'
expect("abc").toBe(731);
expect("ccc").toBe(2109);