JS Console Calendar

calendar.js

let th = {"Su":[],"Mo":[],"Tu":[],"We":[],"Th":[],"Fr":[],"Sa":[]};
const tk = Object.keys(th);
 
const now = new Date();
const month = new Date(now.getFullYear(), now.getMonth()+1, 0);
const daysInMonth = month.getDate();
let moI = month.getDay()-1;
 
// fill days before
for (let i = 0; i < moI; i++) {
  th[tk[i%tk.length]].push(0);
}
 
let max = 0;

[...Array(daysInMonth)].map(x => {
  let s = th[tk[moI%tk.length]];
  s.push(moI-1);
  if (s.length > max) max = s.length;
  moI++
});
 
let rend = [tk.join(' ')];
let rends = [...Array(tk.length)].map(x => []);
 
tk.map(d => {
  let v = th[d];
  const fill = max - v.length;
  
  [...Array(fill)].map(x => v.push(0))
  v.forEach((value,i) => rends[i].push(value))
})
 
for (let i = 0; i < rends.length; i++) {
  rend.push(rends[i]
         .map(d => d == 0 ? " " : d)
         .join(' '))
}
 
console.log(rend)