Convert array of byte values to base64 encoded string and break long lines, Javascript (code golf)

Question

This JavaScript function takes an array of numbers (in the range 0-255) and converts to a base64-encoded string, then breaks long lines if necessary:

functio         


        

Answer 1

I have another entry:

function encode(data)
{
    var str = String.fromCharCode.apply(null,data);
    return btoa(str).replace(/.{76}(?=.)/g,'$&\n');
}

Minified, 88 characters:

function e(d){return btoa(String.fromCharCode.apply(d,d)).replace(/.{76}(?=.)/g,'$&\n')}

Or if you want trailing newlines, 85 characters:

function e(d){return btoa(String.fromCharCode.apply(d,d)).replace(/.{1,76}/g,'$&\n')}

Answer 2

I don't have Firefox handy, so I can't try it out, but from a general string-handling perspective it looks like you have some room to improve. What you're doing is, for every byte, creating a new string one character longer than your previous one. This is an O(N^2) operation. There are a few ways to cut down N so that your algorithm runs in near-linear time:

1. Build up strings to length 57 (this will yield a 76-char Base64 result), then perform a btoa on it and add the resulting string to your output

2. Just like #1, only build an array of lines and call join on it to create the final output string.

3. Use map to create an array of 1-character strings, then call join on it.

Here's some untested code for each method:

function encode(data)
{
  var output = "";
  var str = "";
  for (var i = 0; i < data.length; i++)
  {
    str += String.fromCharCode(data[i]);
    // the "&& i != data.length - 1" clause
    // keeps the extra \n off the end of the output
    // when the last line is exactly 76 characters
    if (str.length == 57 && i != data.length - 1)
    {
      output += btoa(str) + "\n";
      str = "";
    }
  }
  return output + btoa(str);
}

function encode(data)
{
  var output = [];
  var str = "";
  for (var i = 0; i < data.length; i++)
  {
    str += String.fromCharCode(data[i]);
    if (str.length == 57)
    {
      output[output.length] = btoa(str);
      str = "";
    }
  }
  if (str != "")
    output[output.length] = btoa(str);
  return output.join("\n");
}

function encode(data)
{
  var str = data.map(function (d) { return String.fromCharCode(d) }).join("");
  return btoa(str).replace(/.{76}(?=.)/g,'$&\n');
}

And here's the last one, minified (116 chars):

function e(b){return btoa(b.map(function(d){return
String.fromCharCode(d)}).join("")).replace(/.{76}(?=.)/g,'$&\n')}

Answer 3

Works in Firefox 3.6.13:

function encode(data)
{
    var str = data.reduce(function(a,b){ return a+String.fromCharCode(b) },'');
    return btoa(str).replace(/.{76}(?=.)/g,'$&\n');
}