Javascript random string generator with dynamic length and characters type.

javascript-random-string-generator.js

/**
* @link https://stackoverflow.com/a/1349426/11340631
*/

const makeRandomString = (length = 5, typeCharacter = "lowerUpperNumber") => {
  if (length < 5) return "Length must be more than 5.";
  if (
    typeCharacter !== "lower" &&
    typeCharacter !== "upper" &&
    typeCharacter !== "number" &&
    typeCharacter !== "lowerUpper" &&
    typeCharacter !== "lowerNumber" &&
    typeCharacter !== "upperNumber" &&
    typeCharacter !== "lowerUpperNumber"
  ) {
    return "Character type does not match.";
  }

  let characters = "";
  const lower = "abcdefghijklmnopqrstuvwxyz";
  const upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  const number = "0123456789";

  if (typeCharacter === "lower") {
    characters = lower;
  }
  if (typeCharacter === "upper") {
    characters = upper;
  }
  if (typeCharacter === "number") {
    characters = number;
  }
  if (typeCharacter === "lowerUpper") {
    characters = lower + upper;
  }
  if (typeCharacter === "lowerNumber") {
    characters = lower + number;
  }
  if (typeCharacter === "upperNumber") {
    characters = upper + number;
  }
  if (typeCharacter === "lowerUpperNumber") {
    characters = lower + upper + number;
  }

  let result = "";
  const charactersLength = characters.length;
  for (let i = 0; i < length; i++) {
    result += characters.charAt(Math.floor(Math.random() * charactersLength));
  }
  return result;
};