[TypeScript] Base64

Base64.ts

let Base64 = (function () {
  let dic = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

  let encode = (array: Int8Array | Uint8Array | number[]) => {
    let result = [];
    let i = 0;
    while (i < array.length) {
      let b0 = array[i++];
      let b1 = array[i++];
      let b2 = array[i++];
      let en = ((b0 & 0xff) << 16) | ((b1 & 0xff) << 8) | (b2 & 0xff);
      let e0 = (en >> 18) & 0x3f;
      let e1 = (en >> 12) & 0x3f;
      let e2 = (en >> 6) & 0x3f;
      let e3 = en & 0x3f;
      if (b1 === undefined) e2 = 64;
      if (b2 === undefined) e3 = 64;
      result.push(dic.charAt(e0));
      result.push(dic.charAt(e1));
      result.push(dic.charAt(e2));
      result.push(dic.charAt(e3));
    }
    return result.join("");
  };
  let decode = (string: String) => {
    let array = [];
    let i = 0;
    string = string.replace(/[^A-Za-z0-9\+\/\=]/g, "");
    while (i < string.length) {
      let e0 = dic.indexOf(string.charAt(i++));
      let e1 = dic.indexOf(string.charAt(i++));
      let e2 = dic.indexOf(string.charAt(i++));
      let e3 = dic.indexOf(string.charAt(i++));
      let en = (e0 << 18) | (e1 << 12) | (e2 << 6) | e3;
      let b0 = (en >> 16) & 0xff;
      let b1 = (en >> 8) & 0xff;
      let b2 = en & 0xff;
      array.push(b0);
      if (e2 !== 64) array.push(b1);
      if (e3 !== 64) array.push(b2);
    }

    return array;
  };

  let encodeString = (string: String) => {
    return encode([...string].map((it) => it.charCodeAt(0)));
  };

  let decodeString = (string: String) => {
    return String.fromCharCode(...decode(string));
  };
  return { encode, decode, encodeString, decodeString };
})();

export default Base64;