var filename = "mysave.txt"
var contents = "xyz";
document.location = "htmlsave.php?filename=" + filename + "&contents=" + contents;

if(!isset($_GET)) {
    exit(0);
}
$filename = $_GET['filename'];
$contents = $_GET['contents'];

header("Pragma: public"); // required
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private", false); // required for certain browsers
header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename="" . $filename . "";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: " . strlen($contents));
header("Connection: close");
echo $contents;

var i;
var filename = "mysave.txt"
var contents = "";
for(i=0, contents = "";i<10000;i++){
    contents += "x";
}
document.location = "htmlsave.php?filename=" + filename + "&contents=" + contents;

var filename = "mysave.txt"
var contents = "";
for(i=0, contents = "";i<10000;i++){
    contents += "x";
}
dataARR = {
    filename: filename,
    contents: contents
};
var dataJSON = JSON.stringify(dataARR);
$.ajax({
    type: "POST", // This for array
    url: "htmlsave.php",
    async: true,
    cache: false,
    crossDomain: false, // This needs to be true for other people
    data: { myJson: dataJSON },

    success: function (data) {
    },
    error: function (XMLHttpRequest, textStatus, errorThrown) {
    }
});

if(!isset($_POST) || !isset($_POST['myJson'])) {
    exit(0);
}
$dataTotal = json_decode($_POST['myJson'], true);
$filename = $dataTotal['filename'];
$contents = $dataTotal['contents'];

header("Pragma: public"); // required
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private", false); // required for certain browsers
header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename="" . $filename . "";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: " . strlen($contents));
header("Connection: close");
echo $contents;