mpdf没有在ajax调用上工作（从js发送html到php）

mpdf works fine on calling url/ajax_pdf.php directly

but not working on sending html via $.ajax from url/ReportsInterface.js -->url/ajax_pdf.php

no library or file include error . every last function of mdf is working fine

I have tried this code

js

function()
{

var html='<div><p>hello mpdf</p></div>';
$.ajax({
method : "POST",
url : "../common/ajax/ajax_pdf.php",
data : {html :html},
success:function(data){

console.log(data);
}
});

}

php

<?
    session_start();

    include('../../common/libs/mpdf/mpdf.php');

    if($_POST["html"])
{
    $mpdf = new mPDF();
    $mpdf->WriteHTML($_POST["html"]);
    $mpdf->Output($get_data->c_name.".pdf", 'I');
    $mpdf->Output();

}

?>

on console.log html and php contents are generating fine . but is not converting to pdf .. please suggest