Simple phone number compression/decompression functions.

CompressPhoneNumbers.js

/**
 * Compress strings that require only numbers, such as phone numbers.
 *
 * @param {string}  num  Requiring only numbers.
 * @param {string}  code String of symbols used for compression.
 * @return {string} Compressed string
 */
function numCps(
  num,
  code = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
) {
  let radix = code.length;
  let mod;
  let quotient = num.replaceAll(/\D/g, ""); // Remove non-numeric characters.
  let result = "";

  // Encode
  while (quotient > radix) {
    mod = parseInt(quotient) % radix;
    result = code[mod] + result;
    quotient = Math.floor(quotient / radix);
    console.log(
      "quotient: " + quotient + ", mod: " + mod + ", result: " + result
    );
  }
  result = code[quotient] + result;

  return (!num[0] || "0") + result; // If there are leading zeros, write back.
}

/**
 * Undo compressed strings with numCps().
 *
 * @param {string}  num  Compressed by numCps()
 * @param {string}  code Using the same symbol as numCps()
 * @return {string} Original phone number
 */
function numElg(
  num,
  code = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
) {
  let radix, place, index, result;
  place = radix = code.length;
  index = result = 0;

  // Decode
  while (num.length - index) {
    place = radix ** index;
    index++;
    result += code.indexOf(num[num.length - index]) * place;
    console.log(
      "indexOf: " +
        code.indexOf(num[num.length - index]) +
        ", chr: " +
        num[num.length - index] +
        ", " +
        place +
        "の位: " +
        code.indexOf(num[num.length - index]) * place +
        ", result: " +
        result
    );
  }

  return (!num[0] || "0") + result; // If there are leading zeros, write back.
}

CompressPhoneNumbers.min.js

function numCps(n,e="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"){let t,l=e.length,r=n.replaceAll(/\D/g,""),f="";for(;r>l;)t=parseInt(r)%l,f=e[t]+f,r=Math.floor(r/l);return f=e[r]+f,(!n[0]||"0")+f}function numElg(n,e="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"){let t,l,r,f;for(l=t=e.length,r=f=0;n.length-r;)l=t**r,r++,f+=e.indexOf(n[n.length-r])*l;return(!n[0]||"0")+f}

OperationCheck.js

/**
 * Operation check
 */
console.log("=== OUTPUT STERT ===");
console.log("ENCODE RESULT: " + numCps("tel:03-3000-1234"));
console.log("DECODE RESULT: " + numElg(numCps("tel:03-3000-1234")));