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PHP method calls from Javascript not showing up in Wordpress source

I am running a Wordpress website, and trying to call PHP methods from my Javascript code.
When a button is tapped, the saverFoo() Javascript method is called, and attempts to call the PHP method save_image_data().
function saverFoo() {
var dataURL = canvas.toDataURL();
<?php echo save_image_data(dataURL); ?>;
}
function loaderFoo() {
var loadedImage = <?php echo loadimagedata(); ?>;
console.log(loadedImage);
}
The PHP method's implementation is in the function.php file, and is simply attempting to save some image data (dataURL) in the user's meta
function save_image_data($imageData) {
global $current_user;
update_user_meta( $current_user->ID, 'user_design', $_POST['$imageData']);
}
function loadimagedata() {
global $current_user;
$old_notes = get_user_meta($current_user->ID, 'user_design', true);
return $old_notes;
}
Inspecting my web-page in Chrome, shows me an empty space where loaderFoo () (javascript) is supposed to be calling loadimagedata() (php) , and loadedImage is an undefined variable, when I try to log it, such as:
function loaderFoo() {
var loadedImage = ;
console.log(loadedImage);
}
Not sure what fundamental mistake I'm making here.

Always remember that PHP runs on the server side, and javascript on the client side. So we have an order here, the server receives the request PHP processes what it should process and render the page, only here Javascript will be executed.
In this example, when the 'saverFoo()' function is executed, this function <? Php echo save_image_data (dataURL); ?>; has already been written on the page. PHP will not be able to get the information contained in the dataURL variable, not on this way. To do this, we must make a request to the server with this desired information, but with an "image" is not trivial to do this, as there is a limit on the size of the post when using a normal String field.
function saverFoo () {
    var dataURL = canvas.toDataURL ();
    <? php echo save_image_data (dataURL); ?>;
}

PHP doesn't work that way. It is a pre-processor. It is all run and done server side and the resulting text/html/binary data/whatever is sent out to the client. In the case of a content type of text/html the browser will load it, parse it, render it, and run whatever javascript is called.
How you can mix PHP and JavaScript in-line like that would be to use PHP to fill in variables. For example
alert("<?php print($_SERVER['SCRIPT_FILENAME']); ?>");
would work because the client would see
alert("/path/to/foo.php");
and render that for the user.
To really interact with PHP using JavaScript, you'll want to look into using a http based REST type service and perhaps one of the various popular tool sets like Angular, Vue, etc.

How to Pass PHP Session Variable to external JS file in Symfony

Currently I am working in One PHP Symfony Project Regarding the Performance Evaluation of an Employee.
So I need to know how we can get PHP session variable of an employee (Employee Role) Please see the php file ( $role = $_SESSION['empRole']; ) to an external js file.(js file also attached). I am using PHP Symfony framework.
Actually I need to check who is logged in to the website.if it is admin/core members / Hr.
I need to apply validation to some fileds only when the Coremembers login the website.
Here is the code section that I need to pass $role to External JS file(in pastebin)
public function executeIndex(sfWebRequest $request) {
if (isset($_SESSION['empId'])) {
$role = $_SESSION['empRole'];
if ($role == "admin") {
$empId = $this->getUser()->getAttribute('empId');
$team_members = GroupwareEmployeesPeer::getAllSubordinatesId($empId`enter code here`);
$nc = new Criteria();
$nc->add(PeD`enter code here`ates`enter code here`Peer::NAME, 'Dashboard');
$resultset = PeDatesPeer::doSelect($nc);
So Can you guys give me a solution regarding this, since I am stuck with this for a long time.
Please see thepastebin code for php and external js file.
https://pastebin.com/kbkLjSFa - PHP File.
https://pastebin.com/M60Rg64U - JS file

Yes you can get the php variable into the js file.
Method I:
Rename your .js file to .js.php and pass the php variable as a query string to this file where you link this file in your page.
So, if you have some test.js file, rename it to test.js.php and use it in your page like this
<script src="test.js.php?session_var=<?= $your_var_here;?>&any_var=<?= $any_php_var;?>"></script>
And in your js file, retrieve the values from query string parameters
So inside test.js.php, you can simply
var some_var = "<?= $_GET['session_var']";
var any_var = "<?= $_GET['any_var'];?>";
//rest of your logic goes here
Method II:
Use an AJAX request.
var some_var, another_var;
$.ajax({
url : '/url-which-returns-session-vars', //return the session data in json from this url
asnyc : false,
dataType : 'json',
success : function(res){
some_var = res.some_var;
another_var = res.another_var;
}
});
//rest of the logic goes here.
Both of these methods work. But I prefer the first method, since I don't have to write extra code.
Edit:
Suppose the response of the ajax call looks like this
{
some_var : 'value here',
another_var : 'another value here'
}
So res in the success function argument contains this response and since the response is a JSON you can access these values using the . notation.
Thus,
some_var = res.some_var;
another_var = res.another_var;
and since these variables are global variables, you can use them anywhere in your code in this file.

?> <script> var php_variable = '<?php $variable ?>'; </script> <?php
Global variable should be declared before external js file include . in js file access it using this variable name php_variable
After the above code . jquery external file should be included here
<script src="external.js" ></script>
external.js
consol.log(php_variable);

PHP cannot access variable declared in loaded php page with jquery load()

Usually I can get php variables from a different php file declared like this:
$myVar = 'hello';
require 'header.php'
So then in header.php I can use $myVar. But I cannot access a variable that I loaded with ajax in jquery. For example:
index.php:
<html>
<body>
<div id="myDiv"></div>
</body>
</html>
In a script I have:
$(#myDiv).load('newPage.php')
newPage.php :
$myLoadedVar = 'loaded var';
But then I cannot access $myLoadedVar from index.php, is it possible to do this or you cannot access php variables created with ajax ?

PHP is a server-side language while JavaScript is a client-side language. The only way you can get PHP data into JavaScript is by outputting the data in some manner. If you want the full output, just echo it. If you want to load a bunch of simple PHP variables into JavaScript, you can add all the variables you need JS to know about into an array, and then json_encode them.
$firstName = 'John';
$lastName = 'Doe';
$outputArray = array('firstName' => $firstName, 'lastName' => $lastName);
echo json_encode($outputArray);
Then when an ajax function can retrieve this data as an object and you can use result.firstName in JavaScript.
Passing complex items is impossible though, such as those with database connections as properties.

InnerHTML with PHP

I'm trying to run php function inside javascript and pass a parameter to that function but with no luck.
here's my code:
var attribute = 1;
var element = getElementByID('wrapper').innerHTML="<?php echo myfunction("+attribute+");?>";
But the result I'm getting is the output of my function with "+attribute+" added to it, not the proper output of the function.
The function itself is an easy one:
<?php myfunction($attribute){
echo 7+$attribute;
}?>

Php would be executed by the server, but the server isn't involved anymore once your client has started processing javascript. So no, I don't think this is possible.

How to assign a Javascript variable to PHP variable in symfony2?

I am new to web development and I am using symfony2 for this project I am working on.
Have a template file called view.html.php and Inside this I have a JavaScript portion, inside which I want to assign JavaScript variable to PHP variable..I tried to do the following way but it did not work. Could some one please help me out with this.
<script>
....
var temp=json;
//error below
<?php $jsonobj= = temp ?>
...
</script>

in LARGE lines
have your php get your value from a page wich serves this variable via js, then assign it to your php var
understand what i mean ?