Learn !

 

1. function code (start, end, step = 1) {
2.   return new Array(Math.ceil((end.charCodeAt(0) - start.charCodeAt(0))/step))
3.   .fill(start.charCodeAt(0))
4.   .map((x, i) => String.fromCharCode(i*step + start.charCodeAt(0)));
5. }
6. 
   
7. console.log(code('c', 'h', 2));