php into javascript

1$str = <<<MY_MARKER
2<script type="text/javascript">
3  document.write("Hello World!");
4</script>
5MY_MARKER;
6
7echo $str;

1const toSend = {
2            x: 10, 
3            y: 12
4        };
5        const jsonString = JSON.stringify(toSend);
6        const xhr = new XMLHttpRequest();
7
8        xhr.open("POST", "file.php");
9        xhr.setRequestHeader("Content-Type", "application/json");
10        xhr.send(jsonString);
11//php: 
12$request = file_get_contents("php://input");
13$obj = json_decode($request);
14var_dump($obj);