Nano-calendar on javascript without elements rendering (data only)

calendar.js

// Calendar for month `m` of the year `y` with Sunday as first day of week
const calS = (y,m) => { 
  let[r,d,w,l]=[[],1,0,!(y%4)-!(y%1e2)+!(y%4e2)],
      c=((0|23*m/9)+(m<3?y--:y-2)+5+(0|y/4)-(0|y/1e2)+(0|y/4e2))%7;
  for(;d<29+(0x3bbeecc+16*l>>m*2&3);++d,c=++c%7,w+=!c)
    (r[w]||(r[w]=[,,,,,,,]))[c]=d;
  return r
}

// Calendar for month `m` of the year `y` with Monday as first day of week
const calM = (y,m) => {
  let[r,d,w,l]=[[],1,0,!(y%4)-!(y%1e2)+!(y%4e2)],
      c=((0|23*m/9)+(m<3?y--:y-2)+5+(0|y/4)-(0|y/1e2)+(0|y/4e2))%7||7;
  for(;d<29+(0x3bbeecc+16*l>>m*2&3);++d,c=++c%7||7,w+=!(c-1))
    (r[w]||(r[w]=[,,,,,,,]))[c-1]=d;
  return r
}

// Calendar for month `m` of the year `y` with `s` as first day of week
// s=0 - Sunday  s=1 - Monday 
const cal = (y,m,s=0)=>{ 
  let [r,d,w,l]=[[],1,0,!(y%4)-!(y%1e2)+!(y%4e2)],
    c=((0|23*m/9)+(m<3?y--:y-2)+5+(0|y/4)-(0|y/1e2)+(0|y/4e2))%7||(s?7:0);
  for (;d<29+(0x3bbeecc+16*l>>m*2&3);++d,c=++c%7||(s?7:0),w+=!(c-s))
    (r[w]||(r[w]=[,,,,,,,]))[c-s]=d;
  return r;
};



/********* Test *********/

console.log(calS(2020,8));
/*
    [
      [   ,   ,   ,   ,   ,   ,  1 ],
      [  2,  3,  4,  5,  6,  7,  8 ],
      [  9, 10, 11, 12, 13, 14, 15 ],
      [ 16, 17, 18, 19, 20, 21, 22 ],
      [ 23, 24, 25, 26, 27, 28, 29 ],
      [ 30, 31,   ,   ,   ,   ,    ]
    ]
*/

console.log(calM(2020,8));
/*
    [
      [   ,   ,   ,   ,   ,  1,  2 ],
      [  3,  4,  5,  6,  7,  8,  9 ],
      [ 10, 11, 12, 13, 14, 15, 16 ],
      [ 17, 18, 19, 20, 21, 22, 23 ],
      [ 24, 25, 26, 27, 28, 29, 30 ],
      [ 31,   ,   ,   ,   ,   ,    ]
    ]
*/