AJAX

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Text</title>
<script type="text/javascript">
function saveTxt(){
    var theTxt = "Hallo";
    var toUser = "you";

    var xhttp = new XMLHttpRequest();
    xhttp.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
            document.getElementById("demo").innerHTML = this.responseText;
        }
    };

    xhttp.open("POST", "processtext.php", true);
    xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xhttp.send("sometxt=" + theTxt + "&moretxt=" + toUser);
}
</script>
</head>
<body>
<button onclick="saveTxt();">Run script</button>
<div id="demo"></div>
</body>
</html>

<?php
if($_REQUEST["sometxt"]){
    $exampletext = $_REQUEST["sometxt"];
    $secondstring = $_REQUEST["moretxt"];
    echo "The text: ".$exampletext." ".$secondstring;
}
?>