Base64与ArrayBuffer相互转换

通过window.atob和Uint8Array方法

const base64 = "xmE0AcdhNAHHYTQB";
const raw = window.atob(base64);

const uint8Array = new Uint8Array(new ArrayBuffer(raw.length));
uint8Array.forEach((_,i)=>uint8Array[i] = raw.charCodeAt(i));

const arrayBuffer = uint8Array.buffer;

console.log(uint8Array);
console.log(arrayBuffer);

注意：nodejs无atob方法

通过Uint8Array方法

/*
 * base64-arraybuffer
 * https://github.com/niklasvh/base64-arraybuffer
 *
 * Copyright (c) 2012 Niklas von Hertzen
 * Licensed under the MIT license.
 */
(function(){
  "use strict";

  var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  // Use a lookup table to find the index.
  var lookup = new Uint8Array(256);
  for (var i = 0; i < chars.length; i++) {
    lookup[chars.charCodeAt(i)] = i;
  }

  exports.encode = function(arraybuffer) {
    var bytes = new Uint8Array(arraybuffer),
    i, len = bytes.length, base64 = "";

    for (i = 0; i < len; i+=3) {
      base64 += chars[bytes[i] >> 2];
      base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
      base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
      base64 += chars[bytes[i + 2] & 63];
    }

    if ((len % 3) === 2) {
      base64 = base64.substring(0, base64.length - 1) + "=";
    } else if (len % 3 === 1) {
      base64 = base64.substring(0, base64.length - 2) + "==";
    }

    return base64;
  };

  exports.decode =  function(base64) {
    var bufferLength = base64.length * 0.75,
    len = base64.length, i, p = 0,
    encoded1, encoded2, encoded3, encoded4;

    if (base64[base64.length - 1] === "=") {
      bufferLength--;
      if (base64[base64.length - 2] === "=") {
        bufferLength--;
      }
    }

    var arraybuffer = new ArrayBuffer(bufferLength),
    bytes = new Uint8Array(arraybuffer);

    for (i = 0; i < len; i+=4) {
      encoded1 = lookup[base64.charCodeAt(i)];
      encoded2 = lookup[base64.charCodeAt(i+1)];
      encoded3 = lookup[base64.charCodeAt(i+2)];
      encoded4 = lookup[base64.charCodeAt(i+3)];

      bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
      bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
      bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
    }

    return arraybuffer;
  };
})();