index.js

const chars =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

const Base64 = {
  atob: (input = "") => {
    let str = input.replace(/[=]+$/, "");
    let output = "";

    if (str.length % 4 == 1) {
      throw new Error(
        "'atob' failed: The string to be decoded is not correctly encoded."
      );
    }
    for (
      let bc = 0, bs = 0, buffer, i = 0;
      (buffer = str.charAt(i++));
      ~buffer && ((bs = bc % 4 ? bs * 64 + buffer : buffer), bc++ % 4)
        ? (output += String.fromCharCode(255 & (bs >> ((-2 * bc) & 6))))
        : 0
    ) {
      buffer = chars.indexOf(buffer);
    }

    return output;
  },
  btoa: (input = "") => {
    let str = input;
    let output = "";

    for (
      let block = 0, charCode, i = 0, map = chars;
      str.charAt(i | 0) || ((map = "="), i % 1);
      output += map.charAt(63 & (block >> (8 - (i % 1) * 8)))
    ) {
      charCode = str.charCodeAt((i += 3 / 4));

      if (charCode > 0xff) {
        throw new Error(
          "'btoa' failed: The string to be encoded contains characters outside of the Latin1 range."
        );
      }

      block = (block << 8) | charCode;
    }

    return output;
  },
};

export default {
  Base64,
};