js如何實現小程式wx.arrayBufferToBase64方法範例

let buffer = new ArrayBuffer(10);
console.log(buffer);

// 在控制檯上顯示如下
ArrayBuffer(10)
byteLength: 10
[[Prototype]]: ArrayBuffer
[[Int8Array]]: Int8Array(10)
[[Uint8Array]]: Uint8Array(10)
[[Int16Array]]: Int16Array(5)
[[ArrayBufferByteLength]]: 10
[[ArrayBufferData]]: 1367

const myTypedArray = new Uint8Array(buffer)

const str = String.fromCharCode(...myTypedArray)

module.exports = {
  btoa: ...,
  atob: ...
}

const { btoa } =  require('./base64')

var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
  a256 = '',
  r64 = [256],
  r256 = [256],
  i = 0;

var UTF8 = {

  /**
   * Encode multi-byte Unicode string into utf-8 multiple single-byte characters
   * (BMP / basic multilingual plane only)
   *
   * Chars in range U+0080 - U+07FF are encoded in 2 chars, U+0800 - U+FFFF in 3 chars
   *
   * @param {String} strUni Unicode string to be encoded as UTF-8
   * @returns {String} encoded string
   */
  encode: function (strUni) {
    // use regular expressions & String.replace callback function for better efficiency
    // than procedural approaches
    var strUtf = strUni.replace(/[u0080-u07ff]/g, // U+0080 - U+07FF => 2 bytes 110yyyyy, 10zzzzzz
      function (c) {
        var cc = c.charCodeAt(0);
        return String.fromCharCode(0xc0 | cc >> 6, 0x80 | cc & 0x3f);
      })
      .replace(/[u0800-uffff]/g, // U+0800 - U+FFFF => 3 bytes 1110xxxx, 10yyyyyy, 10zzzzzz
        function (c) {
          var cc = c.charCodeAt(0);
          return String.fromCharCode(0xe0 | cc >> 12, 0x80 | cc >> 6 & 0x3F, 0x80 | cc & 0x3f);
        });
    return strUtf;
  },

  /**
   * Decode utf-8 encoded string back into multi-byte Unicode characters
   *
   * @param {String} strUtf UTF-8 string to be decoded back to Unicode
   * @returns {String} decoded string
   */
  decode: function (strUtf) {
    // note: decode 3-byte chars first as decoded 2-byte strings could appear to be 3-byte char!
    var strUni = strUtf.replace(/[u00e0-u00ef][u0080-u00bf][u0080-u00bf]/g, // 3-byte chars
      function (c) { // (note parentheses for precence)
        var cc = ((c.charCodeAt(0) & 0x0f) << 12) | ((c.charCodeAt(1) & 0x3f) << 6) | (c.charCodeAt(2) & 0x3f);
        return String.fromCharCode(cc);
      })
      .replace(/[u00c0-u00df][u0080-u00bf]/g, // 2-byte chars
        function (c) { // (note parentheses for precence)
          var cc = (c.charCodeAt(0) & 0x1f) << 6 | c.charCodeAt(1) & 0x3f;
          return String.fromCharCode(cc);
        });
    return strUni;
  }
};

while (i < 256) {
  var c = String.fromCharCode(i);
  a256 += c;
  r256[i] = i;
  r64[i] = b64.indexOf(c);
  ++i;
}

function code(s, discard, alpha, beta, w1, w2) {
  s = String(s);
  var buffer = 0,
    i = 0,
    length = s.length,
    result = '',
    bitsInBuffer = 0;

  while (i < length) {
    var c = s.charCodeAt(i);
    c = c < 256 ? alpha[c] : -1;

    buffer = (buffer << w1) + c;
    bitsInBuffer += w1;

    while (bitsInBuffer >= w2) {
      bitsInBuffer -= w2;
      var tmp = buffer >> bitsInBuffer;
      result += beta.charAt(tmp);
      buffer ^= tmp << bitsInBuffer;
    }
    ++i;
  }
  if (!discard && bitsInBuffer > 0) result += beta.charAt(buffer << (w2 - bitsInBuffer));
  return result;
}

var Plugin = function (dir, input, encode) {
  return input ? Plugin[dir](input, encode) : dir ? null : this;
};

Plugin.btoa = Plugin.encode = function (plain, utf8encode) {
  plain = Plugin.raw === false || Plugin.utf8encode || utf8encode ? UTF8.encode(plain) : plain;
  plain = code(plain, false, r256, b64, 8, 6);
  return plain + '===='.slice((plain.length % 4) || 4);
};

Plugin.atob = Plugin.decode = function (coded, utf8decode) {
  coded = coded.replace(/[^A-Za-z0-9+/=]/g, "");
  coded = String(coded).split('=');
  var i = coded.length;
  do {
    --i;
    coded[i] = code(coded[i], true, r64, a256, 6, 8);
  } while (i > 0);
  coded = coded.join('');
  return Plugin.raw === false || Plugin.utf8decode || utf8decode ? UTF8.decode(coded) : coded;
};
module.exports = {
  btoa: Plugin.btoa,
  atob: Plugin.atob
}

const { btoa } =  require('./base64')
const arrayBufferToBase64Img = (buffer) => {
  const str = String.fromCharCode(...new Uint8Array(buffer));
  return `data:image/jpeg;base64,${btoa(str)}`;
}