php value to javascript code example

Example 1: javascript php variable

<script type="text/javascript">
   var php_var = "<?php echo $php_var; ?>";
</script>

Example 2: php variable as javascript function parameter in echo

<?php echo "<script> autoFill(".$dropDown.", ".$emptyDropDown."); </script>"; ?>

Example 3: js to php

const toSend = {
            x: 10, 
            y: 12
        };
        const jsonString = JSON.stringify(toSend);
        const xhr = new XMLHttpRequest();

        xhr.open("POST", "file.php");
        xhr.setRequestHeader("Content-Type", "application/json");
        xhr.send(jsonString);
//php: 
$request = file_get_contents("php://input");
$obj = json_decode($request);
var_dump($obj);