Losing chars while sending data by JSONP - php

Question

I want to create a script (javascript file. JS) that I can put from my domain on every website. The script has to read the text from the website and send it to the server. The server is on another domain than the website from which it reads the text, that is why I use JSONP. The read text can be charsed in different ways (different languages – websites from all over the world) and they can be very long that’s why, before sending them I code them by base64, divide them into data packets and send them separately using GET (JSONP).
Without the definition of getJson() function, the code is:
var sBase64Code = base64_encode( document.getElementById('idText').innerHTML );
// we devide sBase64Code into data packets,
// and changing it to array aBase64Code – I skip this algorythm
// and then I send packets to the server in loops
for(i in aBase64Code) {
getJson(['idx='+i, 'code='+aBase64Code[i]], hFunCallback);
}
However, after sending the code to the server, joining the packets and decoding data by base64_decode() it turns out that chars different from English ones are lost.
mb_convert_encoding(base64_decode($b64), mb_detect_encoding(base64_decode($b64))) doesn’t work.
JavaScript base64_encode() function is:
function base64_encode(data) {
var b64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
var o1, o2, o3, h1, h2, h3, h4, bits, i = 0, ac = 0, enc = "", tmp_arr = [];
if(!data) return data;
do {
o1 = data.charCodeAt(i++);
o2 = data.charCodeAt(i++);
o3 = data.charCodeAt(i++);
bits = o1 << 16 | o2 << 8 | o3;
h1 = bits >> 18 & 0x3f;
h2 = bits >> 12 & 0x3f;
h3 = bits >> 6 & 0x3f;
h4 = bits & 0x3f;
tmp_arr[ac++] = b64.charAt(h1) + b64.charAt(h2) + b64.charAt(h3) + b64.charAt(h4);
} while (i < data.length);
enc = tmp_arr.join('');
var r = data.length % 3;
return (r ? enc.slice(0, r - 3) : enc) + '==='.slice(r || 3);
};
Example of sending data:
Base64 from example: WndpbmkZdGEgbmkHIHRvIGtCGWJlay4=