🔑 Generate OTP - A simple TypeScript function to generate a one-time passcode (OTP)

generateOtp.ts

import { randomInt } from "crypto";

interface GenerateOtpOptions {
  /**
   * Chars
   *
   * @description Whether to include A-Z characters in the generated passcode
   * 
   * @default true
   */
  chars: boolean;
  /**
   * Digits
   *
   * @description Whether to include numbers 0-9 in the generated passcode
   * 
   * @default true
   */
  digits: boolean;
  /**
   * Length
   *
   * @description The total length / size of the code to generate
   * 
   * @default 6
   */
  length: number;
}

const digits = "0123456789" as const;
const alphabet = "abcdefghijklmnopqrstuvwxyz" as const;

/**
 * Generate OTP
 *
 * Generates a one-time passcode (OTP) from a provided provided
 * length using chars and/or digits.
 *
 * @param {Object} [options]
 * @param {boolean} [options.chars=true] - Include A-Z characters
 * @param {boolean} [options.digits=true] - Include numbers 0-9
 * @param {boolean} [options.length=6] - Length of the generated string
 */
export function generateOtp(options?: Partial<GenerateOtpOptions>): string {
  const combinedOptions = Object.assign(
    {
      chars: true,
      digits: true,
      length: 6,
    },
    options
  );

  if (combinedOptions.length <= 0)
    throw new Error("OTP length is too short. Please select a longer length.");

  // Build an array of all possible character's to pick from
  const allowedChars: string = [
    ...(combinedOptions.chars ? [alphabet, alphabet.toUpperCase()] : []),
    ...(combinedOptions.digits ? [digits] : []),
  ].join("");

  let token: string = "";

  while (token.length < combinedOptions.length) {
    token += allowedChars[randomInt(0, allowedChars.length)];
  }

  return token;
}