We Keep Coding

Is it possible to reverse final single number output of multiple XOR and bits shifting operations

I have a code written in JS of parsing x,y,z into 1 number.
Is it possible to somehow revert the operation and get x,y,z back by only knowing the final number and the operations made on it?
I have hardcoded x,y,z in the rever function in order to test the reverse process and it works. But what I need is getting the x,y,z back from the parsedOutput
let ParseWithXor = () => {
let x = 25;
let y = 8;
let z = 110;
let finalOutput = 0;
finalOutput = finalOutput ^ (x << 9);
console.log(` finalOutput ^ (${x} << 9) = ${finalOutput}`);
finalOutput = finalOutput ^ (y << 5);
console.log(` finalOutput ^ (${y} << 5) = ${finalOutput}`);
finalOutput = finalOutput ^ z;
console.log(`finalOutput ^ ${z} = ${finalOutput}`);
return finalOutput;
};
let Revert = (parsedOutput) => {
console.log(parsedOutput);
parsedOutput = parsedOutput ^ 110;
console.log(parsedOutput);
parsedOutput = parsedOutput ^ (8 << 5);
console.log(parsedOutput);
parsedOutput = parsedOutput ^ (25 << 9);
console.log(parsedOutput);
};
ParseWithXor();
console.log("-------------------------------------");
Revert(13166);
finalOutput ^ (25 << 9) = 12800
finalOutput ^ (8 << 5) = 13056
finalOutput ^ 110 = 13166
--------------------------------------
13166
13056
12800
0

if you xor an integer with integer twice you will get original number
(a ^ b) ^ b = a
it does not matter the order of xor operations
a ^ b ^ c = b ^ a ^ c
so if you have
a ^ c0 ^ c1 ^ c2 = b
then
a = b ^ c0 ^ c1 ^ c2
so the answer is yes you just xor back in reverse order to obtain the sub results... or in any order if you want just original value.
so you have:
w0 = 0;
w1 = w0 ^ (x << 9);
w2 = w1 ^ (y << 5);
w3 = w2 ^ (z );
I would revers it like this:
w3 = ...;
// x,y,z from w(i) | w(i) from x,y,z
// ---------------------------------------
z = (w3 ^ w2); | w2 = w3 ^ (z );
y = (w2 ^ w1) >> 5; | w1 = w2 ^ (y << 5);
x = (w1 ^ w0) >> 9; | w0 = w1 ^ (x << 9);
// x,y,z from w3,w0 but x,y,z must not overlap bits
// z = <0,31>
// y = <0,15>
// x = <0,(max/512)-1>
// ----------------------------------------------
w = w0 ^ w3;
z = w & 31; w >>= 5;
y = w & 15; w >>= 4;
x = w;

How to do popcount or count bits on arbitrarily long bit sequence in JavaScript

This looks like it works well on integers that are within the max integer size in JavaScript:
function bitCount (n) {
var bits = 0
while (n !== 0) {
bits += bitCount32(n | 0)
n /= 0x100000000
}
return bits
}
function bitCount32 (n) {
n = n - ((n >> 1) & 0x55555555)
n = (n & 0x33333333) + ((n >> 2) & 0x33333333)
return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24
}
I'm wondering though how to count bits generally, on any sized bit stream, efficiently, ideally without converting to string.

The comment with the lookup table, roughly:
var lookup=new Uint8Array(256);
for(var i=0;i<256;i++){
var c=0;
for(var j=i;j;j>>=1)
if(j&1)c++;
lookup[i]=c;
}
function count(arr){
var arr8=new Uint8Array(arr);
return arr8.reduce((a,e)=>a+lookup[e],0);
}
console.log(count(new Uint8Array([0x12,0x34,0x56,0x78,0x9A,0xBC,0xDE,0xF])));
//11 21 22 31 22 32 33 4 = 32
Of course the table-generation could use your magic too.

If you know your buffer will have length divisible by 4,
let array32 = new Uint32Array(buffer);
let numBits = array32.reduce((a, e) => a + bitCount32(e), 0);
Otherwise probably tevemadar's suggestion is better, use Uint8Array and count bits in a byte, not in a dword.

De-interlace bytes

Given an interlaced bit sequence of:
ABABABABABABABAB
What javascript bitwise operation can I use to convert it to be in the sequence:
AAAAAAAABBBBBBBB

That's known as an unshuffle (see also Hacker's Delight 7.2, shuffling bits).
The algorithm given in Hacker's Delight is:
t = (x ^ (x >> 1)) & 0x22222222; x = x ^ t ^ (t << 1);
t = (x ^ (x >> 2)) & 0x0C0C0C0C; x = x ^ t ^ (t << 2);
t = (x ^ (x >> 4)) & 0x00F000F0; x = x ^ t ^ (t << 4);
t = (x ^ (x >> 8)) & 0x0000FF00; x = x ^ t ^ (t << 8);
Those right shifts can be either logical or arithmetic, the AND with the mask ensures that bits affected by that difference do no appear in t anyway.
This is for 32bit numbers, for 16 bit numbers you can chop off the left half of every mask and skip the last step.
This is a sequence of delta swaps, see The Art of Computer Programming volume 4A, Bitwise tricks and techniques, bitswapping.

Check out this algorithm, if it's good for you:
function deinterlace(input) {
var maskOdd = 1;
var maskEven = 2;
var result = 0;
for (var i = 0; i < 8; i++) {
result = result << 1;
if(maskOdd & input) {
result += 1;
}
maskOdd = maskOdd << 2;
}
for (var j = 0; j < 8; j++) {
result = result << 1;
if(maskEven & input) {
result += 1;
console.log(result);
}
}
return result;
}
Working fiddle.

Compressing a blob in javascript

I need to send a blob to the server with ajax, but it can end up getting somewhat large, and I'd like to decrease upload time. I've tried jszip already, but that just gave me an empty file inside the zip. I've also tried btoa(), but it turns out that the encoded value just ends up being [object Blob] instead of the actual blob data. What are my options for compressing blobs?
Here was the code I used for jszip:
var zip = new JSZip();
zip.file("recording.wav", blobFile);
var content = zip.generate();
I then appended "content" to a FormData object and sent it to the server. On the server side, I decoded the POST data (from base64). The zip file opened just fine, but recording.wav was a 0 length file.
Additionally, I've tried using the LZW implementation found here. This was the additional code I used to compress it:
var compressed;
var reader = new FileReader();
reader.onload = function(event){
compressed = LZW.compress(event.target.result);
};
reader.readAsText(blobFile);
However, decompressing it returns null.

Caveat: compressing things like audio files would be better done using an algorithm meant specifically for that type of data, perhaps something lossy. However, knowing how hard it was to find a reasonable lossless implementation as provided below, I'm very concerned that it will be hard to find a good implementation in Javascript for that type of data specifically that meets your needs.
In any case, I've had this general need for compression/decompression in Javascript as well, and I needed the same algorithm to work both client (browser) and server-side (node.js) and I needed it to work on very large files. I had checked out jszip and I also tried that LZW algorithm among at least five or six others none of which satisfied the requirements. I can't remember what the issue was with each specifically, but suffice to say it is surprisingly hard to find a good and FAST compressor/decompressor in javascript that works both server and client side and handles large files! I tried at least a dozen different implementations of various compression algorithms, and finally settled with this one - it hasn't failed me yet!
UPDATE
This is the original source:
https://code.google.com/p/jslzjb/source/browse/trunk/Iuppiter.js?r=2
By someone named Bear - thanks Bear, whoever you are, you're the best.
It is LZJB: http://en.wikipedia.org/wiki/LZJB
UPDATE 2
Corrected a problem with missing semicolon - should not give the object not a function error any longer.
This implementation stops working on data less than about 80 characters in length. So I updated the example to reflect that.
Realized the base64 encode/decode methods are in fact exposed on the object passed in for this version, so...
Currently seeing what we can do about specific blob types - what for example the best approach would be for a image versus audio etc as that would be useful for JS folks in general... will update here with what is found.
UPDATE 3
There is a much better wrapper around the original Iuppiter source from Bear than the one I posted below. It is written by cscott and on github here: https://github.com/cscott/lzjb
I'll be switching to this one, as it does streams as well.
Below is an example in Node.js of its use with a wav file. But before copying the example, let me give you the terrible news first, at least for this one wav file that I tried:
63128 Jun 19 14:09 beep-1.wav
63128 Jun 19 17:47 beep-2.wav
89997 Jun 19 17:47 beep-2.wav.compressed
So it successfully regenerated the wav (and it played). However, the compressed one appears to be larger than the original. Well shoot. In any case, might be good to try on your data, you never know, you might get lucky. Here's the code I used:
var fs = require('fs');
var lzjb = require('lzjb');
fs.readFile('beep-1.wav', function(err, wav){
// base 64 first
var encoded = wav.toString('base64');
// then utf8 - you don't want to go utf-8 directly
var data = new Buffer(encoded, 'utf8');
// now compress
var compressed = lzjb.compressFile(data, null, 9);
// the next two lines are unnecessary, but to see what kind of
// size is written to disk to compare with the original binary file
var compressedBuffer = new Buffer(compressed, 'binary');
fs.writeFile('beep-2.wav.compressed', compressedBuffer, 'binary', function(err) {});
// decompress
var uncompressed = lzjb.decompressFile(compressed);
// decode from utf8 back to base64
var encoded2 = new Buffer(uncompressed).toString('utf8');
// decode back to binary original from base64
var decoded = new Buffer(encoded2, 'base64');
// write it out, make sure it is identical
fs.writeFile('beep-2.wav', decoded, function(err) {});
});
At the end of the day, I think its going to be too difficult to achieve any level of compression on most forms of binary data that isn't clobbered by the resulting base64 encoding. The days of control characters for terminals still haunt us to this day. You could try upping to a different base, but that has its risks and issues as well.
See this for example:
What is the most efficient binary to text encoding?
And this:
Why don't people use base128?
One thing though, definitely before you accept the answer, please please try it out on your blob, I've mainly used it for compressing utf-8, and I'd like to be sure it works on your specific data.
In any case, here it is!
/**
$Id: Iuppiter.js 3026 2010-06-23 10:03:13Z Bear $
Copyright (c) 2010 Nuwa Information Co., Ltd, and individual contributors.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. Neither the name of Nuwa Information nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
$Author: Bear $
$Date: 2010-06-23 18:03:13 +0800 (星期三, 23 六月 2010) $
$Revision: 3026 $
*/
var fastcompressor = {};
(function (k) {
k.toByteArray = function (c) {
var h = [],
b, a;
for (b = 0; b < c.length; b++) a = c.charCodeAt(b), 127 >= a ? h.push(a) : (2047 >= a ? h.push(a >> 6 | 192) : (65535 >= a ? h.push(a >> 12 | 224) : (h.push(a >> 18 | 240), h.push(a >> 12 & 63 | 128)), h.push(a >> 6 & 63 | 128)), h.push(a & 63 | 128));
return h
};
k.Base64 = {
CA: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
CAS: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
IA: Array(256),
IAS: Array(256),
init: function () {
var c;
for (c = 0; 256 > c; c++) k.Base64.IA[c] = -1, k.Base64.IAS[c] = -1;
c = 0;
for (iS = k.Base64.CA.length; c < iS; c++) k.Base64.IA[k.Base64.CA.charCodeAt(c)] = c, k.Base64.IAS[k.Base64.CAS.charCodeAt(c)] = c;
k.Base64.IA["="] = k.Base64.IAS["="] = 0
},
encode: function (c, h) {
var b, a, d, e, m, g, f, l, j;
b = h ? k.Base64.CAS : k.Base64.CA;
d = c.constructor == Array ? c : k.toByteArray(c);
e = d.length;
m = 3 * (e / 3);
g = (e - 1) / 3 + 1 << 2;
a = Array(g);
for (l = f = 0; f < m;) j = (d[f++] & 255) << 16 | (d[f++] & 255) << 8 | d[f++] & 255, a[l++] = b.charAt(j >> 18 & 63), a[l++] = b.charAt(j >> 12 & 63), a[l++] = b.charAt(j >> 6 & 63), a[l++] = b.charAt(j & 63);
f = e - m;
0 < f && (j = (d[m] &
255) << 10 | (2 == f ? (d[e - 1] & 255) << 2 : 0), a[g - 4] = b.charAt(j >> 12), a[g - 3] = b.charAt(j >> 6 & 63), a[g - 2] = 2 == f ? b.charAt(j & 63) : "=", a[g - 1] = "=");
return a.join("")
},
decode: function (c, h) {
var b, a, d, e, m, g, f, l, j, p, q, n;
b = h ? k.Base64.IAS : k.Base64.IA;
c.constructor == Array ? (d = c, m = !0) : (d = k.toByteArray(c), m = !1);
e = d.length;
g = 0;
for (f = e - 1; g < f && 0 > b[d[g]];) g++;
for (; 0 < f && 0 > b[d[f]];) f--;
l = "=" == d[f] ? "=" == d[f - 1] ? 2 : 1 : 0;
a = f - g + 1;
j = 76 < e ? ("\r" == d[76] ? a / 78 : 0) << 1 : 0;
e = (6 * (a - j) >> 3) - l;
a = Array(e);
q = p = 0;
for (eLen = 3 * (e / 3); p < eLen;) n = b[d[g++]] << 18 | b[d[g++]] <<
12 | b[d[g++]] << 6 | b[d[g++]], a[p++] = n >> 16 & 255, a[p++] = n >> 8 & 255, a[p++] = n & 255, 0 < j && 19 == ++q && (g += 2, q = 0);
if (p < e) {
for (j = n = 0; g <= f - l; j++) n |= b[d[g++]] << 18 - 6 * j;
for (b = 16; p < e; b -= 8) a[p++] = n >> b & 255
}
if (m) return a;
for (n = 0; n < a.length; n++) a[n] = String.fromCharCode(a[n]);
return a.join("")
}
};
k.Base64.init();
NBBY = 8;
MATCH_BITS = 6;
MATCH_MIN = 3;
MATCH_MAX = (1 << MATCH_BITS) + (MATCH_MIN - 1);
OFFSET_MASK = (1 << 16 - MATCH_BITS) - 1;
LEMPEL_SIZE = 256;
k.compress = function (c) {
var h = [],
b, a = 0,
d = 0,
e, m, g = 1 << NBBY - 1,
f, l, j = Array(LEMPEL_SIZE);
for (b = 0; b < LEMPEL_SIZE; b++) j[b] =
3435973836;
c = c.constructor == Array ? c : k.toByteArray(c);
for (b = c.length; a < b;) {
if ((g <<= 1) == 1 << NBBY) {
if (d >= b - 1 - 2 * NBBY) {
f = b;
for (d = a = 0; f; f--) h[d++] = c[a++];
break
}
g = 1;
m = d;
h[d++] = 0
}
if (a > b - MATCH_MAX) h[d++] = c[a++];
else if (e = (c[a] + 13 ^ c[a + 1] - 13 ^ c[a + 2]) & LEMPEL_SIZE - 1, l = a - j[e] & OFFSET_MASK, j[e] = a, e = a - l, 0 <= e && e != a && c[a] == c[e] && c[a + 1] == c[e + 1] && c[a + 2] == c[e + 2]) {
h[m] |= g;
for (f = MATCH_MIN; f < MATCH_MAX && c[a + f] == c[e + f]; f++);
h[d++] = f - MATCH_MIN << NBBY - MATCH_BITS | l >> NBBY;
h[d++] = l;
a += f
} else h[d++] = c[a++]
}
return h
};
k.decompress = function (c,
h) {
var b, a = [],
d, e = 0,
m = 0,
g, f, l = 1 << NBBY - 1,
j;
b = c.constructor == Array ? c : k.toByteArray(c);
for (d = b.length; e < d;) {
if ((l <<= 1) == 1 << NBBY) l = 1, f = b[e++];
if (f & l)
if (j = (b[e] >> NBBY - MATCH_BITS) + MATCH_MIN, g = (b[e] << NBBY | b[e + 1]) & OFFSET_MASK, e += 2, 0 <= (g = m - g))
for (; 0 <= --j;) a[m++] = a[g++];
else break;
else a[m++] = b[e++]
}
if (!("undefined" == typeof h ? 0 : h)) {
for (b = 0; b < m; b++) a[b] = String.fromCharCode(a[b]);
a = a.join("")
}
return a
}
})(fastcompressor);
And if memory serves... here's how you use it:
var compressed = fastcompressor.compress("0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"); // data less than this length poses issues.
var decompressed = fastcompressor.decompress(compressed);
Rgds....Hoonto/Matt
Also, what I've posted is minified but beautified, and very slightly adapted for ease-of-use. Check the link in the update above for the original stuff.

JS Zip will work fine just correct your syntax..
function create_zip() {
var zip = new JSZip();
zip.add("recording.wav", blobfile);//here you have to give blobFile in the form of raw bits >> convert it in json notation.. or stream ..
zip.add("hello2.txt", "Hello Second World\n");//this is optional..
content = zip.generate();
location.href="data:application/zip;base64," + content;
}
you can add multiple files too..
Just zip.file will become zip.add
and then zip.generate() will do the rest.. as you have done,
or refer old Post its last part of JavaScript, and NativeBridge will be helpful if you can utilize, in this post user records using Objective C that you can ignore, but sends this object using JavaScript and Socket that you can/may utilize..
I hope this will do ... :)

How to decode byte of array data using javascript [duplicate]

How do I convert a byte array into a string?
I have found these functions that do the reverse:
function string2Bin(s) {
var b = new Array();
var last = s.length;
for (var i = 0; i < last; i++) {
var d = s.charCodeAt(i);
if (d < 128)
b[i] = dec2Bin(d);
else {
var c = s.charAt(i);
alert(c + ' is NOT an ASCII character');
b[i] = -1;
}
}
return b;
}
function dec2Bin(d) {
var b = '';
for (var i = 0; i < 8; i++) {
b = (d%2) + b;
d = Math.floor(d/2);
}
return b;
}
But how do I get the functions working the other way?
Thanks.
Shao

You need to parse each octet back to number, and use that value to get a character, something like this:
function bin2String(array) {
var result = "";
for (var i = 0; i < array.length; i++) {
result += String.fromCharCode(parseInt(array[i], 2));
}
return result;
}
bin2String(["01100110", "01101111", "01101111"]); // "foo"
// Using your string2Bin function to test:
bin2String(string2Bin("hello world")) === "hello world";
Edit: Yes, your current string2Bin can be written more shortly:
function string2Bin(str) {
var result = [];
for (var i = 0; i < str.length; i++) {
result.push(str.charCodeAt(i).toString(2));
}
return result;
}
But by looking at the documentation you linked, I think that the setBytesParameter method expects that the blob array contains the decimal numbers, not a bit string, so you could write something like this:
function string2Bin(str) {
var result = [];
for (var i = 0; i < str.length; i++) {
result.push(str.charCodeAt(i));
}
return result;
}
function bin2String(array) {
return String.fromCharCode.apply(String, array);
}
string2Bin('foo'); // [102, 111, 111]
bin2String(string2Bin('foo')) === 'foo'; // true

ES6 update
Now, string 'foo' also equals
String.fromCharCode(...[102, 111, 111])
Original answer
Simply apply your byte array to String.fromCharCode. For example
String.fromCharCode.apply(null, [102, 111, 111])
equals 'foo'.
MDN docs here.
Caveat: works for arrays shorter than 65535 - MDN docs here.

Try the new Text Encoding API:
// create an array view of some valid bytes
let bytesView = new Uint8Array([104, 101, 108, 108, 111]);
console.log(bytesView);
// convert bytes to string
// encoding can be specfied, defaults to utf-8 which is ascii.
let str = new TextDecoder().decode(bytesView);
console.log(str);
// convert string to bytes
// encoding can be specfied, defaults to utf-8 which is ascii.
let bytes2 = new TextEncoder().encode(str);
// look, they're the same!
console.log(bytes2);
console.log(bytesView);

This should work:
String.fromCharCode(...array);
Or
String.fromCodePoint(...array)

That string2Bin can be written even more succinctly, and without any loops, to boot!
function string2Bin ( str ) {
return str.split("").map( function( val ) {
return val.charCodeAt( 0 );
} );
}

String to byte array: "FooBar".split('').map(c => c.charCodeAt(0));
Byte array to string: [102, 111, 111, 98, 97, 114].map(c => String.fromCharCode(c)).join('');

I think this would be more efficient:
function toBinString (arr) {
var uarr = new Uint8Array(arr.map(function(x){return parseInt(x,2)}));
var strings = [], chunksize = 0xffff;
// There is a maximum stack size. We cannot call String.fromCharCode with as many arguments as we want
for (var i=0; i*chunksize < uarr.length; i++){
strings.push(String.fromCharCode.apply(null, uarr.subarray(i*chunksize, (i+1)*chunksize)));
}
return strings.join('');
}

Even if I'm a bit late, I thought it would be interesting for future users to share some one-liners implementations I did using ES6.
One thing that I consider important depending on your environment or/and what you will do with with the data is to preserve the full byte value. For example, (5).toString(2) will give you 101, but the complete binary conversion is in reality 00000101, and that's why you might need to create a leftPad implementation to fill the string byte with leading zeros. But you may not need it at all, like other answers demonstrated.
If you run the below code snippet, you'll see the first output being the conversion of the abc string to a byte array and right after that the re-transformation of said array to it's corresponding string.
// For each byte in our array, retrieve the char code value of the binary value
const binArrayToString = array => array.map(byte => String.fromCharCode(parseInt(byte, 2))).join('')
// Basic left pad implementation to ensure string is on 8 bits
const leftPad = str => str.length < 8 ? (Array(8).join('0') + str).slice(-8) : str
// For each char of the string, get the int code and convert it to binary. Ensure 8 bits.
const stringToBinArray = str => str.split('').map(c => leftPad(c.charCodeAt().toString(2)))
const array = stringToBinArray('abc')
console.log(array)
console.log(binArrayToString(array))

If your array is encoded in UTF-8 and you can't use the TextDecoder API because it is not supported on IE:
You can use the FastestSmallestTextEncoderDecoder polyfill recommended by the Mozilla Developer Network website;
You can use this function also provided at the MDN website:
function utf8ArrayToString(aBytes) {
var sView = "";
for (var nPart, nLen = aBytes.length, nIdx = 0; nIdx < nLen; nIdx++) {
nPart = aBytes[nIdx];
sView += String.fromCharCode(
nPart > 251 && nPart < 254 && nIdx + 5 < nLen ? /* six bytes */
/* (nPart - 252 << 30) may be not so safe in ECMAScript! So...: */
(nPart - 252) * 1073741824 + (aBytes[++nIdx] - 128 << 24) + (aBytes[++nIdx] - 128 << 18) + (aBytes[++nIdx] - 128 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
: nPart > 247 && nPart < 252 && nIdx + 4 < nLen ? /* five bytes */
(nPart - 248 << 24) + (aBytes[++nIdx] - 128 << 18) + (aBytes[++nIdx] - 128 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
: nPart > 239 && nPart < 248 && nIdx + 3 < nLen ? /* four bytes */
(nPart - 240 << 18) + (aBytes[++nIdx] - 128 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
: nPart > 223 && nPart < 240 && nIdx + 2 < nLen ? /* three bytes */
(nPart - 224 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
: nPart > 191 && nPart < 224 && nIdx + 1 < nLen ? /* two bytes */
(nPart - 192 << 6) + aBytes[++nIdx] - 128
: /* nPart < 127 ? */ /* one byte */
nPart
);
}
return sView;
}
let str = utf8ArrayToString([50,72,226,130,130,32,43,32,79,226,130,130,32,226,135,140,32,50,72,226,130,130,79]);
// Must show 2H₂ + O₂ ⇌ 2H₂O
console.log(str);

If you are using node.js you can do this:
yourByteArray.toString('base64');

Too late to answer but if your input is in form of ASCII bytes, then you could try this solution:
function convertArrToString(rArr){
//Step 1: Convert each element to character
let tmpArr = new Array();
rArr.forEach(function(element,index){
tmpArr.push(String.fromCharCode(element));
});
//Step 2: Return the string by joining the elements
return(tmpArr.join(""));
}
function convertArrToHexNumber(rArr){
return(parseInt(convertArrToString(rArr),16));
}

I had some decrypted byte arrays with padding characters and other stuff I didn't need, so I did this (probably not perfect, but it works for my limited use)
var junk = String.fromCharCode.apply(null, res).split('').map(char => char.charCodeAt(0) <= 127 && char.charCodeAt(0) >= 32 ? char : '').join('');

> const stringToBin = (str) => [...str].map(item=>item.charCodeAt())
> undefined
> stringToBin('hello')
> (5) [104, 101, 108, 108, 111]
> const binToString = (array) => String.fromCharCode(...array)
> undefined
> binToString(stringToBin('hello'))
> 'hello'

What you are looking for is String.fromCharCode
What you want to do is loop through the array of bytes (represented as integers), create the string equivalent and add it to the result:
function bin2String(array) {
var result = "";
for (const char of array) {
result += String.fromCharCode(char);
}
return result;
}
console.log(bin2String([116, 104, 101, 32, 114, 101, 115, 117, 108, 116]));
You can also use the Array.Map function to convert the array of bytes into an array of strings, then join them all.
function string2Bin(array) {
return array.map(byte => String.fromCharCode(byte)).join("");
}
console.log(string2Bin([116, 104, 101, 32, 114, 101, 115, 117, 108, 116]));

UPDATE
#rosberg-linhares posted best solution so far to handle UTF8.
Didn't find any solution that would work with UTF-8 characters. String.fromCharCode is good until you meet 2 byte character.
For example word Hüser can come over the wire in form of arraybuffer as [0x48,0xc3,0xbc,0x73,0x65,0x72] (e.g. through websocket connection)
But if you go through it with String.fromCharCode you will have Hüser as each byte will be converted to a char separately, and letter ü is encoded in two bytes.
Solution
Currently I'm using following solution:
function pad(n) { return (n.length < 2 ? '0' + n : n); }
function decodeUtf8(data) {
return decodeURIComponent(
data.map(byte => ('%' + pad(byte.toString(16)))).join('')
);
}

The simplest solution I've found is:
var text = atob(byteArray);