Converting byte array to string in javascript

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);