How to pass content in tinymce's textarea to a PHP file directly instead of via ajax?

Build a simple webpage ebeded TinyMCE.

The html part.

<form method="post" action="dump.php">
<div id="main">
<div id="container_left">
        <textarea id="mytextarea"></textarea>
        <input id="submit" type="submit" value="submit">            
</div>
<div id="show_right"></div>
</div>
</form>

The javascript part.

<script src="tinymce/tinymce.min.js"></script>
<script type="text/javascript">
tinymce.init({
    selector: "textarea",
    height: 250,
    plugins: [
        "code advlist autolink lists link image charmap print preview anchor",
        "searchreplace visualblocks code fullscreen",
        "insertdatetime media table contextmenu paste"
    ],
    toolbar: "code insertfile undo redo | styleselect | bold italic | alignleft aligncenter alignright alignjustify | bullist numlist outdent indent | link image",
    setup: function (editor) {
        editor.on('init keydown change', function (e) {
           document.getElementById('show_right').innerText = editor.getContent();
        });
    }
});
</script>

Now i want to print content in the TinyMCE's editor , after you click the submit button.

The dump.php

<?php
    print_r($_POST);
?>

Why nothing print by dump.php?
I can send info to the dump.php via ajax method.
1.Remove <form method="post" action="dump.php"></form> in html part.
2.Add the following js code in the javascript part.

<script>
function send(){
    var data = tinyMCE.get('mytextarea').getContent();
    var ajax = new XMLHttpRequest();
    ajax.open('POST','dump.php',false);
    ajax.setRequestHeader('Content-type','application/x-www-form-urlencoded');
    ajax.send('data='+data);    
} 
ob = document.getElementById("submit");
ob.addEventListener("click",send);
</script>

I have tried that it can pass content which i type in the textarea whose id is mytextarea to dump.php and dump.php can print the array properly.

My issue is to pass content in tinymce's textarea to a PHP file directly ,instead of via ajax?
Do the work without ajax.

from How to pass content in tinymce's textarea to a PHP file directly instead of via ajax?