@nithin-sivakumar/genotp/index.js

A lightweight and secure OTP (One-Time Password) generator for JavaScript with customizable features like length, character set, prefix, suffix, and base64 encoding.

import crypto from "crypto";

class OTPGenerator {
  /**
   * Generate an OTP with secure randomness.
   * @param {number} length - Length of the OTP (default: 6).
   * @param {string} mode - Mode of OTP generation: 'numeric', 'alphanumeric', or 'custom' (default: 'numeric').
   * @param {string} charSet - Custom character set to use (only for 'custom' mode).
   * @param {string} prefix - Optional prefix to be added to the OTP (default: "").
   * @param {string} suffix - Optional suffix to be added to the OTP (default: "").
   * @param {boolean} base64Encode - Whether to return the OTP in base64 encoding (default: false).
   * @returns {string} The generated OTP.
   */
  static generate(
    length = 6,
    mode = "numeric",
    charSet = "",
    prefix = "",
    suffix = "",
    base64Encode = false
  ) {
    const predefinedCharSets = {
      numeric: "0123456789",
      alphanumeric: "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
      custom: charSet,
    };

    const finalCharSet = predefinedCharSets[mode] || predefinedCharSets.numeric;

    if (
      !finalCharSet ||
      typeof finalCharSet !== "string" ||
      finalCharSet.length === 0
    ) {
      throw new Error("Invalid character set or mode.");
    }

    if (length <= 0) {
      throw new Error("Length must be greater than 0.");
    }

    const otp = Array.from(crypto.randomFillSync(new Uint8Array(length)))
      .map((byte) => finalCharSet[byte % finalCharSet.length])
      .join("");

    const fullOtp = `${prefix}${otp}${suffix}`;

    if (base64Encode) {
      return Buffer.from(fullOtp).toString("base64"); // Return base64 encoded OTP
    }

    return fullOtp;
  }
}

export const generate = OTPGenerator.generate;