We Keep Coding

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.

Is it possible to store a JavaScript function that returns a string in a php variable?

something like :
<?php
$phpVar = "<script> function jsFunc(){ return 'Hello world';} </script>";
?>
is that even possible? if no, is there a way to do same thing?
If Ajax is the only solution, how do I retrieve a value of an input and store it as a php variable?
I tried something like this and it doesn't work.
<input type=text value="hello" id="myInput">
<?php
$phpVar = "<script>
function jsFunc(){
var inputVal = $('#myInput').val();
return inputVal;
}
</script>";
?>

PHP runs at server side and JS in the browser (apart node and related technologies).
Only way you can do something similar would be do to render from PHP in your HTML a tag <script> </script> and add you JS function and executing it there.
Al thought I would definitely not suggest it.

you can store this string in variable. for php interpreter it will be just a text string, nothing else. but when browser receives this data, string will be recognized as js function.
UPDATE
in this case easiest way for send data from browser to server is use a form. there is many examples in the web how to do it.

How To Pass Arguments to Javascript File From PHP Exec

After a form is submitted from my php file it checks it, and then is supposed to call an exec function that will execute a binary file using the second file listed in the code. Shown below:
if (isset($_POST['admin']) && !empty($_POST['admin'])) {
echo exec('/home/mainshee/public_html/wp-content/themes/twentyseventeen/phantom/phantomjs-directory/bin/phantomjs /home/mainshee/public_html/wp-content/themes/twentyseventeen/phantom/phantomjs-directory/examples/bigdaddy.js');
}
The problem here is that the preceding javascript file bigdaddy.js has to take three arguments of its own in order to function. To solve this issue, I tried the following:
echo exec('/home/mainshee/public_html/wp-content/themes/twentyseventeen/phantom/phantomjs-directory/bin/phantomjs /home/mainshee/public_html/wp-content/themes/twentyseventeen/phantom/phantomjs-directory/examples/bigdaddy.js' $_POST['admin'] $_POST['user'] $_POST['password']);
This bricked my site.
Does anybody have any ideas how this may be done? All of the possible solutions I have found detail PHP to PHP, NOT PHP to Javascript. Thanks all!

you have to post back the javascript variable to your server before the server can handle the value. To do this you can either program a javascript function that submits a form - or you can use ajax / jquery. jQuery.post
Maybe the most easiest approach for you is something like this
function myJavascriptFunction() {
var javascriptVariable = "John";
window.location.href = "myphpfile.php?name=" + javascriptVariable;
}
On your myphpfile.php you can use $_GET['name'] after your javascript was executed.

How to use xml pass the data to javascript by DHTMLX

I use DHTMLX. I want to use the ajax component get the data from php, the php will create the xml. How to get this xml data into javascript.
enter code here
dhtmlxAjax.get("php/getUsername.php", function(r){
r = r.xmlDoc.responseXML; // will give you DOM object
//console.log(r.firstChild.tagName);
alert(r.firstChild.tagName("param1"));
});
thank you

Just use the php echo function to echo the php variable into a java script variable.
eg. If you have a php variable called $XMLData you would do the following
var XMLdata = <?php echo $XMLData; ?>
Then on page load your php variable becomes a javascript variable and can be used. from anywhere in javascript provided that the variable is within its scope.

I can't get a value from a PHP array...?

I'm writing a script to retrieve the scores from an osu! beatmap. The script uses the osu! API, which can be found here. I've obtained a valid API key, and got the info from the website. My project can be found here: failosu!.
This script is called by AJAX, and the variable s is passed via POST.
My problem is with the returned array.
In the following snippet (not really, it's pretty much my entire script), I make a request for the beatmap information first. In doing this, I am passing a variable, s (beatmap set ID), to the server, and trying to get the variable b (beatmap ID).
However, whenever I call $d1['beatmap_id'], it doesn't return anything to the main page. Instead, my AJAX script runs the error function rather than the success function. Does anyone know what my problem is?
if($_POST['id']) {
$s = $_POST['id'];
$k = "xxxxxxxxxxxxxxxxxxxxxxxxxxxx";
$u0 = "https://osu.ppy.sh/api/get_beatmaps?k=".$k."&s=".$s;
$d0 = json_decode(file_get_contents($u0));
$d1 = get_object_vars($d0[0]);
$b = $d1["beatmap_id"];
// THE CODE STOPS WORKING HERE FOR SOME REASON ????
$u = "https://osu.ppy.sh/api/get_scores?k=".$k."&b=".$b."&m=0";
echo $u;
$d = json_decode(file_get_contents($u));
for($i=0;$i<count($d);$i++) {
echo "<li>".$i." ".$d[$i]['username']."</li>";
}
}
Does anyone know what's wrong? Do you need me to tell you more information about my code?