JSFiddle - React, Tailwind, and code Playground

JavaScript

function parse(x)
{
    if(x<10)return x;
    else if(x<36)return String.fromCharCode(x+55).toUpperCase();
    else if(x<62)return String.fromCharCode(x+29).toLowerCase();
    else return "z";
}

var res="";
for(var a=-10;a<70;a++)res+=a+" -> "+parse(a)+"\n";
alert(res);