pako string compression to/from base64 in a browser

compress.js

import pako from 'pako';

// Usage: 
// console.log(compress('hello'), decompress(compress('hello')));

export function compress(str) {
  var unit8arr = pako.deflate(str);
  return base64EncArr(unit8arr);
}

export function decompress(base64) {
  var uint8arr = base64DecToArr(base64);
  return pako.inflate(uint8arr, { to: 'string' });
}


// The following functions are expert from https://developer.mozilla.org/en-US/docs/Glossary/Base64
function b64ToUint6(nChr) {
  return nChr > 64 && nChr < 91 ? nChr - 65
    : nChr > 96 && nChr < 123 ? nChr - 71
    : nChr > 47 && nChr < 58 ? nChr + 4
    : nChr === 43 ? 62
    : nChr === 47 ? 63 : 0;
}

function base64DecToArr(sBase64, nBlocksSize) {
  const sB64Enc = sBase64.replace(/[^A-Za-z0-9+/]/g, "");
  const nInLen = sB64Enc.length;
  const nOutLen = nBlocksSize ? 
    Math.ceil(((nInLen * 3 + 1) >> 2) / nBlocksSize) * nBlocksSize : (nInLen * 3 + 1) >> 2;
  const taBytes = new Uint8Array(nOutLen);

  let nMod3, nMod4, nUint24 = 0, nOutIdx = 0;
  for (let nInIdx = 0; nInIdx < nInLen; nInIdx++) {
    nMod4 = nInIdx & 3;
    nUint24 |= b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << (6 * (3 - nMod4));
    if (nMod4 === 3 || nInLen - nInIdx === 1) {
      nMod3 = 0;
      while (nMod3 < 3 && nOutIdx < nOutLen) {
        taBytes[nOutIdx] = (nUint24 >>> ((16 >>> nMod3) & 24)) & 255;
        nMod3++;
        nOutIdx++;
      }
      nUint24 = 0;
    }
  }

  return taBytes;
}

/* Base64 string to array encoding */
function uint6ToB64(nUint6) {
  return nUint6 < 26 ? nUint6 + 65
    : nUint6 < 52 ? nUint6 + 71
    : nUint6 < 62 ? nUint6 - 4
    : nUint6 === 62 ? 43
    : nUint6 === 63 ? 47 : 65;
}

function base64EncArr(aBytes) {
  let nMod3 = 2, sB64Enc = "";

  const nLen = aBytes.length;
  let nUint24 = 0;
  for (let nIdx = 0; nIdx < nLen; nIdx++) {
    nMod3 = nIdx % 3;

    nUint24 |= aBytes[nIdx] << ((16 >>> nMod3) & 24);
    if (nMod3 === 2 || aBytes.length - nIdx === 1) {
      sB64Enc += String.fromCodePoint(
        uint6ToB64((nUint24 >>> 18) & 63),
        uint6ToB64((nUint24 >>> 12) & 63),
        uint6ToB64((nUint24 >>> 6) & 63),
        uint6ToB64(nUint24 & 63)
      );
      nUint24 = 0;
    }
  }
  return (
    sB64Enc.substring(0, sB64Enc.length - 2 + nMod3) +
    (nMod3 === 2 ? "" : nMod3 === 1 ? "=" : "==")
  );
}