excel_column_naming.js

var nextChar = c=>c?String.fromCharCode(c.charCodeAt(0)+1):'A';
var nextCol = s=>s.replace(/([^Z]?)(Z*)$/, (_,a,z)=>nextChar(a) + z.replace(/Z/g,'A'));

//test:

nextCol(''); //A
nextCol('A'); //B
nextCol('Z'); //AA
nextCol('AA'); //AB
nextCol('XYZ'); //XZA
nextCol('ZZZZ'); //AAAAA

//output: A,B,C,...,ZZ
for(var i=0, s=''; i<702; i++){
    s = nextCol(s);
    console.log(s);
}

//output: A,B,C,...,ZZZZ
for(var i=0, s=''; i<475254; i++){
    s = nextCol(s);
    console.log(s);
}