Develop Reference

Google Closure Compiler inlines a repeatedly used private property - a flaw or am I missing something?

I found a JavaScript base64 encoder/decoder some time ago on StackOverflow. It looks something like this:
var Base64 = {
// private property
_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
// private method for UTF-8 encoding
_utf8_encode : function (string) {
string = string.replace(/\r\n/g,"\n");
var utftext = "";
for (var n = 0; n < string.length; n++) {
var c = string.charCodeAt(n);
if (c < 128) {
utftext += String.fromCharCode(c);
}
else if((c > 127) && (c < 2048)) {
utftext += String.fromCharCode((c >> 6) | 192);
utftext += String.fromCharCode((c & 63) | 128);
}
else {
utftext += String.fromCharCode((c >> 12) | 224);
utftext += String.fromCharCode(((c >> 6) & 63) | 128);
utftext += String.fromCharCode((c & 63) | 128);
}
}
return utftext;
},
// private method for UTF-8 decoding
_utf8_decode : function (utftext) {
var string = "";
var i = 0;
var c = c1 = c2 = 0;
while ( i < utftext.length ) {
c = utftext.charCodeAt(i);
if (c < 128) {
string += String.fromCharCode(c);
i++;
}
else if((c > 191) && (c < 224)) {
c2 = utftext.charCodeAt(i+1);
string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
i += 2;
}
else {
c2 = utftext.charCodeAt(i+1);
c3 = utftext.charCodeAt(i+2);
string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
i += 3;
}
}
return string;
},
// public method for encoding
encode : function (input){
var output = "";
var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
var i = 0;
input = this._utf8_encode(input);
while (i < input.length) {
chr1 = input.charCodeAt(i++);
chr2 = input.charCodeAt(i++);
chr3 = input.charCodeAt(i++);
enc1 = chr1 >> 2;
enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
enc4 = chr3 & 63;
if (isNaN(chr2)) {
enc3 = enc4 = 64;
} else if (isNaN(chr3)) {
enc4 = 64;
}
output = output +
this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
}
return output;
}
// public method for decoding
decode : function (input) {
var output = "";
var chr1, chr2, chr3;
var enc1, enc2, enc3, enc4;
var i = 0;
input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
while (i < input.length) {
enc1 = this._keyStr.indexOf(input.charAt(i++));
enc2 = this._keyStr.indexOf(input.charAt(i++));
enc3 = this._keyStr.indexOf(input.charAt(i++));
enc4 = this._keyStr.indexOf(input.charAt(i++));
chr1 = (enc1 << 2) | (enc2 >> 4);
chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
chr3 = ((enc3 & 3) << 6) | enc4;
output = output + String.fromCharCode(chr1);
if (enc3 != 64) {
output = output + String.fromCharCode(chr2);
}
if (enc4 != 64) {
output = output + String.fromCharCode(chr3);
}
}
output = this._utf8_decode(output);
return output;
}
};
I modified it to something like this:
var Base64 = (function(){
var _keyStr = /* ... */;
function _utf8_encode(string) {
/* ... */
}
function _utf8_decode(utftext) {
/* ... */
}
function encode(input){
/* ... */
}
function decode(input){
/* ... */
}
return {
"encode" : encode,
"decode" : decode
}
})();
Should be the same right? And I have a bonus for not opposing "private" methods and property.
Then I make it go through Google Closure Compiler's "simple optimization" (actually I used this compressor but the output is the same). To my surprise, it compiles to something like this (prettified a little bit to make it more readable):
var Base64=function(){
return{encode:function(b){
/* ... */
d=d+"ABCDE...+/=".charAt(a)+/* ... */
},decode:function(b){
/* ... */
a="ABCDE...+/=".indexOf(/* ... */
}};
}();
This seems very un-compressing, because the content of _keyStr is repeated many times in those two functions, effectively making the code larger. Not to mention the closure now seems pointless.
I tried to change the minified version to this:
var Base64=function(){
var z="ABCDE...+/=";
return{encode:function(b){
/* ... */
d=d+z.charAt(a)+/* ... */
},decode:function(b){
/* ... */
a=z.indexOf(/* ... */
}};
}();
And did a few test and it seems it's working.
But I'm not sure if I accidentally broke something, because in my experience, Closure Compiler do respect "private" function, and would not "inline" a private function if it's referred multiple times.
So my question is, is it OK to add back the private property here? Is this a minor flaw in Closure Compiler or am I missing something?

This is covered in the Closure Compiler FAQ:
https://github.com/google/closure-compiler/wiki/FAQ#closure-compiler-inlined-all-my-strings-which-made-my-code-size-bigger-why-did-it-do-that
There are cases where inlining a string will make code size larger post-gzip, but I don't expect that will be the case here as it is unlikely to "flood" the gzip compression window.

Base64 - File is damaged

I'm trying to upload a pdf file through javascript. I have the base64 representation of the file and I decode it. The file is uploaded but that data seems to be corrupt.
The error message says "The file is damaged and could not be repaired" when I try opening the file.
I get the base64 string server side like so...
byte[] buffer = new byte[length];
var postedFile = httpRequest.Files[file];
postedFile.InputStream.Read(buffer, 0, length);
string encodedString = Convert.ToBase64String(buffer);
Here is the ajax call I make to upload the file
var data= Base64.decode(result); //result is the base64 encoded string
$.ajax({
url: url,
type: "POST",
data: data,
processData: false,
headers: {
"accept": "application/json;odata=verbose",
"X-RequestDigest": _digetsValue,
"content-length": length
},
success: function (data)
{
alert("it worked");
},
error: function (err)
{
}
});
For decoding, I'm using this chunk of code...
or from here How can you encode a string to Base64 in JavaScript?
var Base64 = {
// private property
_keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
// public method for encoding
encode: function (input)
{
var output = "";
var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
var i = 0;
input = Base64._utf8_encode(input);
while (i < input.length)
{
chr1 = input.charCodeAt(i++);
chr2 = input.charCodeAt(i++);
chr3 = input.charCodeAt(i++);
enc1 = chr1 >> 2;
enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
enc4 = chr3 & 63;
if (isNaN(chr2))
{
enc3 = enc4 = 64;
} else if (isNaN(chr3))
{
enc4 = 64;
}
output = output +
Base64._keyStr.charAt(enc1) + Base64._keyStr.charAt(enc2) +
Base64._keyStr.charAt(enc3) + Base64._keyStr.charAt(enc4);
}
return output;
},
// public method for decoding
decode: function (input)
{
var output = "";
var chr1, chr2, chr3;
var enc1, enc2, enc3, enc4;
var i = 0;
input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
while (i < input.length)
{
enc1 = Base64._keyStr.indexOf(input.charAt(i++));
enc2 = Base64._keyStr.indexOf(input.charAt(i++));
enc3 = Base64._keyStr.indexOf(input.charAt(i++));
enc4 = Base64._keyStr.indexOf(input.charAt(i++));
chr1 = (enc1 << 2) | (enc2 >> 4);
chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
chr3 = ((enc3 & 3) << 6) | enc4;
output = output + String.fromCharCode(chr1);
if (enc3 != 64)
{
output = output + String.fromCharCode(chr2);
}
if (enc4 != 64)
{
output = output + String.fromCharCode(chr3);
}
}
output = Base64._utf8_decode(output);
return output;
},
// private method for UTF-8 encoding
_utf8_encode: function (string)
{
string = string.replace(/\r\n/g, "\n");
var utftext = "";
for (var n = 0; n < string.length; n++)
{
var c = string.charCodeAt(n);
if (c < 128)
{
utftext += String.fromCharCode(c);
}
else if ((c > 127) && (c < 2048))
{
utftext += String.fromCharCode((c >> 6) | 192);
utftext += String.fromCharCode((c & 63) | 128);
}
else
{
utftext += String.fromCharCode((c >> 12) | 224);
utftext += String.fromCharCode(((c >> 6) & 63) | 128);
utftext += String.fromCharCode((c & 63) | 128);
}
}
return utftext;
},
// private method for UTF-8 decoding
_utf8_decode: function (utftext)
{
var string = "";
var i = 0;
var c = c1 = c2 = 0;
while (i < utftext.length)
{
c = utftext.charCodeAt(i);
if (c < 128)
{
string += String.fromCharCode(c);
i++;
}
else if ((c > 191) && (c < 224))
{
c2 = utftext.charCodeAt(i + 1);
string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
i += 2;
}
else
{
c2 = utftext.charCodeAt(i + 1);
c3 = utftext.charCodeAt(i + 2);
string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
i += 3;
}
}
return string;
}
}
Originally, I was doing something like this...
getFileBuffer = function (file)
{
var deferred = $.Deferred();
var reader = new FileReader();
reader.onload = function (e)
{
deferred.resolve(e.target.result);
}
reader.onerror = function (e)
{
deferred.reject(e.target.error);
}
reader.readAsArrayBuffer(file);
return deferred.promise();
};
But of course this is exclusive to HTML5 and whatnot. So when I would call my ajax function, I would pass in this arraybuffer from the file reader and voila! It would work. Now I'm trying to mimic the same sort of functionality with IE8. Is this possible?
Thanks

I wrote some functions a while ago I believe to be binary safe, here are the relevant ones for you; base64To6 and (perhaps poorly named) base6To8.
var chars = (
'ABCDEFGHIJKLMNOPQRSTUVWXYZ' +
'abcdefghijklmnopqrstuvwxyz' +
'0123456789+/'
),
inver = {}, i;
for (i = 0; i < chars.length; ++i) {
inver[chars[i]] = i;
}
function base64To6(b64) {
var arr6 = [],
i = b64.length, lenMod = 0;
while (b64.charAt(--i) === '=')
++lenMod;
for (i = 0; i < b64.length - lenMod; ++i)
arr6.push(inver[b64.charAt(i)]);
i = b64.length & 3;
if (i) i = 4 - i;
i = i + b64.length;
arr6.byteLength = 3 * i / 4 - lenMod;
return arr6;
}
function base6To8(arr6) {
var arr8 = [], i,
e1, e2, e3,
s1, s2, s3, s4,
d1, d2, d3, d4;
for (i = 0; i < arr6.length; i += 4) {
s1 = (d1 = arr6[i] ) & 63;
s2 = (d2 = arr6[i + 1]) & 63;
s3 = (d3 = arr6[i + 2]) & 63;
s4 = (d4 = arr6[i + 3]) & 63;
// xxxxxx xxyyyy yyyyzz zzzzzz
e1 = ( s1 << 2) + (s2 >>> 4);
e2 = ((s2 & 15) << 4) + (s3 >>> 2);
e3 = ((s3 & 3) << 6) + s4 ;
arr8.push(e1);
if (d3 !== undefined)
arr8.push(e2, e3);
else if (d2 !== undefined )
arr8.push(e2);
}
if (arr6.byteLength !== undefined)
arr8.length = +arr6.byteLength;
return arr8;
}
Now if you do
var int8arr = base6to8(base64to6(data));
You will have an Array of Integers (at most 8 bit numbers), which the Base64 was representing. JavaScript does not use Int8 for Number so you can't immediately use this Array.
Unfortunately, as far as I know, IE8 does not support UInt8Array or Blob, which would let you then happily work with the binary data, so I'm not sure exactly where you'd want to take it from here.

Create file and invoke download using JavaScript

I want to dynamically create a JSON file in my JS code and also invoke the download of that file?
Any chance I can do that in JavaScript?
THANKS!!

Either use a server side language and GET vars (don't forget to set the MIME type to something like application/octet-stream) or base64 encode the JSON into a Data URI if you aren't worried about supporting legacy browsers.
Here's an example; try writing some text and then pressing download. Only problem is you can't control the filename:
<!DOCTYPE HTML>
<html>
<head>
<title>Data URI</title>
<script>
var Base64 = {
// private property
_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
// public method for encoding
encode : function (input) {
var output = "";
var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
var i = 0;
input = Base64._utf8_encode(input);
while (i < input.length) {
chr1 = input.charCodeAt(i++);
chr2 = input.charCodeAt(i++);
chr3 = input.charCodeAt(i++);
enc1 = chr1 >> 2;
enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
enc4 = chr3 & 63;
if (isNaN(chr2)) {
enc3 = enc4 = 64;
} else if (isNaN(chr3)) {
enc4 = 64;
}
output = output +
this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
}
return output;
},
// public method for decoding
decode : function (input) {
var output = "";
var chr1, chr2, chr3;
var enc1, enc2, enc3, enc4;
var i = 0;
input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
while (i < input.length) {
enc1 = this._keyStr.indexOf(input.charAt(i++));
enc2 = this._keyStr.indexOf(input.charAt(i++));
enc3 = this._keyStr.indexOf(input.charAt(i++));
enc4 = this._keyStr.indexOf(input.charAt(i++));
chr1 = (enc1 << 2) | (enc2 >> 4);
chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
chr3 = ((enc3 & 3) << 6) | enc4;
output = output + String.fromCharCode(chr1);
if (enc3 != 64) {
output = output + String.fromCharCode(chr2);
}
if (enc4 != 64) {
output = output + String.fromCharCode(chr3);
}
}
output = Base64._utf8_decode(output);
return output;
},
// private method for UTF-8 encoding
_utf8_encode : function (string) {
string = string.replace(/\r\n/g,"\n");
var utftext = "";
for (var n = 0; n < string.length; n++) {
var c = string.charCodeAt(n);
if (c < 128) {
utftext += String.fromCharCode(c);
}
else if((c > 127) && (c < 2048)) {
utftext += String.fromCharCode((c >> 6) | 192);
utftext += String.fromCharCode((c & 63) | 128);
}
else {
utftext += String.fromCharCode((c >> 12) | 224);
utftext += String.fromCharCode(((c >> 6) & 63) | 128);
utftext += String.fromCharCode((c & 63) | 128);
}
}
return utftext;
},
// private method for UTF-8 decoding
_utf8_decode : function (utftext) {
var string = "";
var i = 0;
var c = c1 = c2 = 0;
while ( i < utftext.length ) {
c = utftext.charCodeAt(i);
if (c < 128) {
string += String.fromCharCode(c);
i++;
}
else if((c > 191) && (c < 224)) {
c2 = utftext.charCodeAt(i+1);
string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
i += 2;
}
else {
c2 = utftext.charCodeAt(i+1);
c3 = utftext.charCodeAt(i+2);
string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
i += 3;
}
}
return string;
}
}
window.onload=function(){
document.getElementById('download').onclick=function(){
window.open("data:application/octet-stream;base64,"+Base64.encode(document.getElementById('text').value));
}
}
</script>
</head>
<body style="margin:0;padding:0;overflow:hidden;">
<textarea id="text"></textarea>
<input type="button" value="Download" style="height:auto;width:100px" id="download"/>
</body>
</html>

Yes you can, but you need to create this file as a string.
Then, call:
window.location = window.URL.createObjectURL(new Blob([what_is_in_your_file], {type: "application/json"}));

Base64 decoding is not working for binary data

well I need a Base64 decoding function. But it is not returning desired output when i am working with binary data. I know atob and atob functions but my problem is I am implementing it in workers and the user agent chrome. chrome not at implemented atob, btoa functions in workers, so suggest me a base64 functions that works with binary data. Now I am using the below function it is not working for binary data.
var Base64 = {
// private property
_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
// public method for encoding
encode : function (input) {
var output = "";
var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
var i = 0;
input = Base64._utf8_encode(input);
while (i < input.length) {
chr1 = input.charCodeAt(i++);
chr2 = input.charCodeAt(i++);
chr3 = input.charCodeAt(i++);
enc1 = chr1 >> 2;
enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
enc4 = chr3 & 63;
if (isNaN(chr2)) {
enc3 = enc4 = 64;
} else if (isNaN(chr3)) {
enc4 = 64;
}
output = output +
this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
}
return output;
},
// public method for decoding
decode : function (input) {
var output = "";
var chr1, chr2, chr3;
var enc1, enc2, enc3, enc4;
var i = 0;
input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
while (i < input.length) {
enc1 = this._keyStr.indexOf(input.charAt(i++));
enc2 = this._keyStr.indexOf(input.charAt(i++));
enc3 = this._keyStr.indexOf(input.charAt(i++));
enc4 = this._keyStr.indexOf(input.charAt(i++));
chr1 = (enc1 << 2) | (enc2 >> 4);
chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
chr3 = ((enc3 & 3) << 6) | enc4;
output = output + String.fromCharCode(chr1);
if (enc3 != 64) {
output = output + String.fromCharCode(chr2);
}
if (enc4 != 64) {
output = output + String.fromCharCode(chr3);
}
}
output = Base64._utf8_decode(output);
return output;
},
// private method for UTF-8 encoding
_utf8_encode : function (string) {
string = string.replace(/\r\n/g,"\n");
var utftext = "";
for (var n = 0; n < string.length; n++) {
var c = string.charCodeAt(n);
if (c < 128) {
utftext += String.fromCharCode(c);
}
else if((c > 127) && (c < 2048)) {
utftext += String.fromCharCode((c >> 6) | 192);
utftext += String.fromCharCode((c & 63) | 128);
}
else {
utftext += String.fromCharCode((c >> 12) | 224);
utftext += String.fromCharCode(((c >> 6) & 63) | 128);
utftext += String.fromCharCode((c & 63) | 128);
}
}
return utftext;
},
// private method for UTF-8 decoding
_utf8_decode : function (utftext) {
var string = "";
var i = 0;
var c = c1 = c2 = 0;
while ( i < utftext.length ) {
c = utftext.charCodeAt(i);
if (c < 128) {
string += String.fromCharCode(c);
i++;
}
else if((c > 191) && (c < 224)) {
c2 = utftext.charCodeAt(i+1);
string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
i += 2;
}
else {
c2 = utftext.charCodeAt(i+1);
c3 = utftext.charCodeAt(i+2);
string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
i += 3;
}
}
return string;
}
}
Thanks in advance!!

I did a quick search and found a decoder that claims to decode binary data, though I have not tried it:
https://github.com/danguer/blog-examples/blob/master/js/base64-binary.js

Silverlight to Javascript interop UTF encoding/decoding

How do I get both alerts, one invoked from silverlight and the other invoked from javascript, to show the same data in the same way.
eg. ���� != ýÿýÿý
System.Windows.Browser.HtmlPage.Window.Alert( data );
alert(parameters);
Silverlight3 code, sending data to javascript function:
System.Windows.Browser.HtmlPage.Window.Alert( data );
// data contains binary data read from files
data = Convert.ToBase64String(Encoding.UTF8.GetBytes(data));
HtmlPage.Window.Eval("var data='"+data+"'makePOSTRequest('"+this.url+"',data);");
javascript function:
function makePOSTRequest(url,parameters)
{
...
parameters = UTF8.encode(decode64(parameters));
alert(parameters);
...
}
javascript library:
var UTF8 = {
// public method for url encoding
encode: function(string) {
string = string.replace(/\r\n/g, "\n");
var utftext = "";
for (var n = 0; n < string.length; n++) {
var c = string.charCodeAt(n);
if (c < 128) {
utftext += String.fromCharCode(c);
}
else if ((c > 127) && (c < 2048)) {
utftext += String.fromCharCode((c >> 6) | 192);
utftext += String.fromCharCode((c & 63) | 128);
}
else {
utftext += String.fromCharCode((c >> 12) | 224);
utftext += String.fromCharCode(((c >> 6) & 63) | 128);
utftext += String.fromCharCode((c & 63) | 128);
}
}
return utftext;
},
// public method for url decoding
decode: function(utftext) {
var string = "";
var i = 0;
var c = c1 = c2 = 0;
while (i < utftext.length) {
c = utftext.charCodeAt(i);
if (c < 128) {
string += String.fromCharCode(c);
i++;
}
else if ((c > 191) && (c < 224)) {
c2 = utftext.charCodeAt(i + 1);
string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
i += 2;
}
else {
c2 = utftext.charCodeAt(i + 1);
c3 = utftext.charCodeAt(i + 2);
string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
i += 3;
}
}
return string;
}
}
var keyStr = "ABCDEFGHIJKLMNOP" +
"QRSTUVWXYZabcdef" +
"ghijklmnopqrstuv" +
"wxyz0123456789+/" +
"=";
function encode64(input) {
var output = "";
var chr1, chr2, chr3 = "";
var enc1, enc2, enc3, enc4 = "";
var i = 0;
do {
chr1 = input.charCodeAt(i++);
chr2 = input.charCodeAt(i++);
chr3 = input.charCodeAt(i++);
enc1 = chr1 >> 2;
enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
enc4 = chr3 & 63;
if (isNaN(chr2)) {
enc3 = enc4 = 64;
} else if (isNaN(chr3)) {
enc4 = 64;
}
output = output +
keyStr.charAt(enc1) +
keyStr.charAt(enc2) +
keyStr.charAt(enc3) +
keyStr.charAt(enc4);
chr1 = chr2 = chr3 = "";
enc1 = enc2 = enc3 = enc4 = "";
} while (i < input.length);
return output;
}
function decode64(input) {
var output = "";
var chr1, chr2, chr3 = "";
var enc1, enc2, enc3, enc4 = "";
var i = 0;
// remove all characters that are not A-Z, a-z, 0-9, +, /, or =
var base64test = /[^A-Za-z0-9\+\/\=]/g;
if (base64test.exec(input)) {
alert("There were invalid base64 characters in the input text.\n" +
"Valid base64 characters are A-Z, a-z, 0-9, �+�, �/�, and �=�\n" +
"Expect errors in decoding.");
}
input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
do {
enc1 = keyStr.indexOf(input.charAt(i++));
enc2 = keyStr.indexOf(input.charAt(i++));
enc3 = keyStr.indexOf(input.charAt(i++));
enc4 = keyStr.indexOf(input.charAt(i++));
chr1 = (enc1 << 2) | (enc2 >> 4);
chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
chr3 = ((enc3 & 3) << 6) | enc4;
output = output + String.fromCharCode(chr1);
if (enc3 != 64) {
output = output + String.fromCharCode(chr2);
}
if (enc4 != 64) {
output = output + String.fromCharCode(chr3);
}
chr1 = chr2 = chr3 = "";
enc1 = enc2 = enc3 = enc4 = "";
} while (i < input.length);
return output;
}

Do you need to UTF-8 encode your characters, or do you just need a way to get these characters into the JavaScipt string? I would recommend using unicode escape sequences (see Unicode at at Mozilla Developer Center). For example, the copyright character is represented as "\u00A9". The nice thing about unicode escape sequences is they can exist in a source file that is encoded using iso-8859-1, but still allow for any unicode character.
See Converting Unicode strings to escaped ascii string for an example of how to do generate these escape sequences in C#.

You seem to be encoding the data as UTF-8 twice, you do it in silverlight:-
Encoding.UTF8.GetBytes(data)
and you do it again in Javascript
parameters = UTF8.encode(decode64(parameters));
are you sure this line shouldn't be:-
parameters = UTF8.decode(decode64(parameters));
?
Is there a reason you're not using WebClient or WebRequest inside Silverlight to do this posting?