Convert excel column alphabet (e.g. AA) to number (e.g., 25)

Question

In my grid the column headers are named A,B,C...,AA,AB,AC,...etc like an excel spreadsheet. How can I convert the string to number like: A => 1, B =>

Answer 1

I rewrote Yoshi's answer in a more verbose form that explains better how it works and is easier to port to other languages:

var foo = function(val) {
    var base = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
    var baseNumber = base.length;

    var runningTotal = 0;
    var characterIndex = 0;
    var indexExponent = val.length - 1;

    while( characterIndex < val.length ){
        var digit = val[characterIndex];
        var digitValue = base.indexOf(digit) + 1;
        runningTotal += Math.pow(baseNumber, indexExponent) * digitValue;

        characterIndex += 1
        indexExponent -= 1
    }

    return runningTotal;
};

console.log(['A', 'AA', 'AB', 'ZZ'].map(foo)); // [1, 27, 28, 702]