AJAX with PHP encoding issue

My whole website is UTF-8 encoded, all my files (.JS, .HTML, .PHP) are saved in UTF-8 (no BOM).

I always use
header('Content-Type: text/html; charset=UTF-8');
at the beggining of my PHP files.

I also use
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
for my HTML files.

But I still have an encoding issue...

I have an AJAX request that send me data to output in the DOM...

This is my PHP file that answers to the AJAX requests:
<?php
header('Content-Type: text/html; charset=UTF-8');

if (array_key_exists('str', $_GET))
$myStr = $_GET['str'];
else
$myStr = '';

echo($myStr);
?>

This is the JavaScript that do the AJAX request:
function TestUTF()
{
var request = CreateRequest();
var unicodeTest = document.getElementById('unicodeTest');
if (request != null && unicodeTest)
{
unicodeTest = unicodeTest.value;
var ajaxUrl = 'test-ajax.php?str=' + escape(unicodeTest);

request.open('POST', ajaxUrl, true);
request.onreadystatechange = function(){TestRS(request)};
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
request.send(null);
}
}

function TestRS(request)
{
if (request.readyState == 4)
{
if (request.status == 200)
{
var ajaxResults = document.getElementById('ajaxResults');
if (ajaxResults)
{
var newP = document.createElement('p');
newP.appendChild(document.createTextNode('AJAX write : ' + request.responseText));
ajaxResults.appendChild(newP);
}
}
else
alert('HTTP status ' + request.status);
}
}

TestUTF();

As you can see this is a really simple project that get UTF-8 data for an HTML <input> element, sends it's value (content) through JavaScript then it's processed by PHP and then written back to the HTML (via the DOM) with JavaScript.

As far as I can see it's the PHP that screw my UTF-8 string... How can it be? I'm telling the browser that it's UTF-8 with header.

If I add utf8_encode to the echo all is right, but the purpose of this test is to get rid of these utf8_encode.

Anyone can help? I can provide full sources of this sample project if you want to try it.

Thanks!

Found my solution!

Use encodeURIComponent instead of escape in JavaScript!

Why does (JavaScript) escape do mess the string encoding when in UTF-8???

I found out that escape only works with ASCII chars. When using Unicode (UTF-8) data with it, the output is corrupted. It even crash IE JavaScript andd XML engine.