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

solution 1: best performance and browser compatibility

// convert A to 1, Z to 26, AA to 27
function lettersToNumber(letters){
    var chrs = ' ABCDEFGHIJKLMNOPQRSTUVWXYZ', mode = chrs.length - 1, number = 0;
    for(var p = 0; p < letters.length; p++){
        number = number * mode + chrs.indexOf(letters[p]);
    }
    return number;
}

solution 2: best performance and compatibility and shorter code (Recommended)

// convert A to 1, Z to 26, AA to 27
function lettersToNumber(letters){
    for(var p = 0, n = 0; p < letters.length; p++){
        n = letters[p].charCodeAt() - 64 + n * 26;
    }
    return n;
}

solution 3: short code (es6 arrow function)

// convert A to 1, Z to 26, AA to 27
function lettersToNumber(letters){
    return letters.split('').reduce((r, a) => r * 26 + parseInt(a, 36) - 9, 0);
}

test:

['A', 'Z', 'AA', 'AB', 'ZZ','BKTXHSOGHKKE'].map(lettersToNumber);
// [1, 26, 27, 28, 702, 9007199254740991]

lettersToNumber('AAA'); //703