小程序Base64字符串编解码

var Base64 = {

// private property
_keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="

// public method for encoding
, encode (input) {
  let output = "";
  let chr1; let chr2; let chr3; let enc1; let enc2; let enc3; let enc4;
  let i = 0;

  input = Base64._utf8_encode(input);

  while (i < input.length) {
    chr1 = input.charCodeAt(i++);
    chr2 = input.charCodeAt(i++);
    chr3 = input.charCodeAt(i++);

    enc1 = chr1 >> 2;
    enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
    enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
    enc4 = chr3 & 63;

    if (isNaN(chr2)) {
      enc3 = enc4 = 64;
    }
    else if (isNaN(chr3)) {
      enc4 = 64;
    }

    output = output +
      this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
      this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
  } // Whend

  return output;
} // End Function encode


// public method for decoding
, decode (input) {
  let output = "";
  let chr1; let chr2; let chr3;
  let enc1; let enc2; let enc3; let enc4;
  let i = 0;

  input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
  while (i < input.length) {
    enc1 = this._keyStr.indexOf(input.charAt(i++));
    enc2 = this._keyStr.indexOf(input.charAt(i++));
    enc3 = this._keyStr.indexOf(input.charAt(i++));
    enc4 = this._keyStr.indexOf(input.charAt(i++));

    chr1 = (enc1 << 2) | (enc2 >> 4);
    chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
    chr3 = ((enc3 & 3) << 6) | enc4;

    output += String.fromCharCode(chr1);

    if (enc3 != 64) {
      output += String.fromCharCode(chr2);
    }

    if (enc4 != 64) {
      output += String.fromCharCode(chr3);
    }

  } // Whend

  output = Base64._utf8_decode(output);

  return output;
} // End Function decode


// private method for UTF-8 encoding
, _utf8_encode (string) {
  let utftext = "";
  string = string.replace(/\r\n/g, "\n");

  for (let n = 0; n < string.length; n++) {
    const c = string.charCodeAt(n);

    if (c < 128) {
      utftext += String.fromCharCode(c);
    }
    else if ((c > 127) && (c < 2048)) {
      utftext += String.fromCharCode((c >> 6) | 192);
      utftext += String.fromCharCode((c & 63) | 128);
    }
    else {
      utftext += String.fromCharCode((c >> 12) | 224);
      utftext += String.fromCharCode(((c >> 6) & 63) | 128);
      utftext += String.fromCharCode((c & 63) | 128);
    }

  } // Next n

  return utftext;
} // End Function _utf8_encode

// private method for UTF-8 decoding
, _utf8_decode (utftext) {
  let string = "";
  let i = 0;
  let c; let c1; let c2; let c3;
  c = c1 = c2 = 0;

  while (i < utftext.length) {
    c = utftext.charCodeAt(i);

    if (c < 128) {
      string += String.fromCharCode(c);
      i++;
    }
    else if ((c > 191) && (c < 224)) {
      c2 = utftext.charCodeAt(i + 1);
      string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
      i += 2;
    }
    else {
      c2 = utftext.charCodeAt(i + 1);
      c3 = utftext.charCodeAt(i + 2);
      string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
      i += 3;
    }

  } // Whend

  return string;
} // End Function _utf8_decode

}

export{
Base64
};