hbarcalcchecksum = (accoundid, ledgerid)->
  checksum = ""
  
  # 0 = mainnet
  # 1 = stable testnet
  # 2 = previewnet
  # ledgerid = 1
  
  a = "0.0." + accoundid.toString()
  d = a.split("").map (i)-> if i == "." then 10 else Number i
  
  h = [ledgerid, 0,0,0,0,0,0]
  
  p3 = 26 * 26 * 26
  p5 = 26 * 26 * 26 * 26 * 26
  
  sd0 = d.filter((i,idx)-> (idx % 2) == 0).reduce((a,b)-> a+b) %11
  sd1 = d.filter((i,idx)-> (idx % 2) == 1).reduce((a,b)-> a+b) %11
  
  sd = d.reduce ((acc, curr) -> (acc * 31 + curr) % p3), 0
  sh = h.reduce ((acc, curr) -> (acc * 31 + curr) % p5), 0
  
  c = ((((d.length % 5) * 11 + sd0) * 11 + sd1) * p3 + sd + sh) % p5
  cp = (c * 1000003) % p5
  
  
  while cp > 0
    checksum = String.fromCharCode((cp % 26) + 97) + checksum
    cp = Math.floor(cp / 26)
  
  # Ensure checksum is 5 characters long
  checksum = 'a'.repeat(5 - checksum.length) + checksum
  checksum

In this way, the checksum can be calculated from the hbar account ID. The checksum is essential to determine shard or realm, test or production environment. It will be a requirement in the future.