index.html

<html>
    <head>
        <title>Form</title>
    </head>
    <body>
    
    <form id="myForm">
 <textarea id="str" name="str" rows="10" cols="50">According to a researcher at Cambridge University, it doesn't matter in what order the letters in a word are, the only important thing is that the first and last letter be at the right place. The rest can be a total mess and you can still read it without problem. This is because the human mind does not read every letter by itself but the word as a whole</textarea>        
        <input type="submit" name="submit" value="Submit Form" />
    </form>
    
    <div id="postData"></div>
    
     <script src="http://code.jquery.com/jquery-1.9.1.js"></script>
    <script type="text/javascript">
    $(document).ready(function(){
        $('#myForm').submit(function(e){
            e.preventDefault();
            $.ajax({
                url: "post.php",
                type: "POST",
                data: $(this).serialize(),
                success: function(data){
                    $("#postData").html(data);
                },
                error: function(){
                    alert("Form submission failed!");
                }
            });
        });
    });
    </script>
    </body>
</html>