TS create random string custom length custom prefix

CreateRandomPrefixedCustomLengthString.ts

const alphanum = "aAbBcCdDeEfFgGHhIIJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789".split("");

export const random: (size: number, prefix: string | null) => string = (size, prefix = null) => {
  if(prefix && prefix.length > size) return throw("size must be greater than prefix length")
  const result = [];
  for (let i = 0; i < size; i++) {
    result.push(alphanum[Math.floor(Math.random() * alphanum.length)]);
  }
  const base = result.join("");
  if (!prefix) return base;
  return `${prefix}:${base.substr(0, base.length - prefix.length)}`;
};