JavaScript functions for music related conversions

musicalConversions.js

let pitchclassToKeyString = function(k) {  
  ks = Math.floor(k/2); 
  ks += (k > 4 && k%2 == 1) ? 1 : 0; 
  ks %= 5; ks += k > 8 ? 65 : 67; 
  var keystr = String.fromCharCode(ks); 
  keystr += ((k<5 && k%2==1)||(k>5&&k%2==0)) ? "#" : "";
  return keystr
}

let keyStringToPitchclass = function(k) {
  const acc = k[1] == "#" ? "sharp" : k[1] == "b" ? "flat" : "natural";
  let pc = (((k.charCodeAt(0) - 53) % 7) * 2); pc += pc > 4 ? -1 : 0; 
  pc += acc === "sharp" ? 1 : acc === "flat" ? -1 : 0; 
  pc %= 12; pc += pc < 0 ? 12 : 0;
  return pc
}

let midiToFrequency = function(midinote) {
  return 440.0 * Math.pow( 2.0, (midinote - 69.0) / 12.0 );
}

let frequencyToMidi = function(freq) {
  return 12 * Math.log2(freq/440) + 69; }
}