PHP: Read an html file and get access to JS variable

Question

Lets say I have a public html page on the internet with the following content:

<html>
    <head>
        <script>
            var variableA = {
                name: "A"
            };
            variableA.id = 1;
        </script>
    </head>
    <body>
        ...
    </body>
</html>

Is there a way to get the value of the variable variableA with php?

Something like this:

$html = file_get_contents($myUrl);
$variableA = magicMethodIamLookingFor("variableA");
print_r($variableA);

With this result:

Array(
    "name" => "A",
    "id" => 1
)

I could do it just with regex and json_decode (similar like How to get Javascript variable from an HTML page?) but the problem is, that its not just a single json, but there are also variable changes like variableA.id = 1;

Possible duplicate of How to get Javascript variable from an HTML page? — Mohammad
– Mohammad, Commented Nov 7, 2018 at 11:35
You can for example send the variable value in a form or simply create an HTTP request and send it as URL parameter. In both cases, the target URL will be your PHP script. — David Ferenczy Rogožan
– David Ferenczy Rogožan, Commented Nov 7, 2018 at 11:45
@DawidFerenczy: I have no access on the public url. @Mohammad: That would be possible, but since the variable is change (variableA.id = 1;) it will be really tricky to do that that way — bernhardh
– bernhardh, Commented Nov 7, 2018 at 14:31
I'm not getting it. What's on the "public url"? Do you mean that you can't modify the HTML page by that? — David Ferenczy Rogožan
– David Ferenczy Rogožan, Commented Nov 7, 2018 at 15:08

Vimal Maheedharan · Accepted Answer · 2018-11-08 10:51:05Z

Note: With plain PHP scripting, it is not possible to access JS vars.

Interesting requirement. Below goes a solution. Lets consider the case if the variable name is passed in the URL. Let the page name be 'index.php'. The browsing URL looks like this localhost/index.php?varName=variableA, where varName is the query param which takes variable name as value. We can pass comma separated values also by tweaking the code a bit. But that is not considered now.

Outlining the steps below

Get contents of url.php and place it in a hidden div of index.php
Beneath the captured content, call an Ajax function with var name & var value as param.
Inside the ajax page, save the name / value to some DB or file.

After the ajax call there is some more DOM where we will print the name / value & remove the record from DB or File after displaying the same. NB: The main code is in JS - See getVarWithValue(variable) function.

<html>
<body>

    <?php 
        $varName = (isset($_GET['varName']) && trim($_GET['varName']) != "") ? $_GET['varName'] : 'variableA';
    ?>

    <div style="display:none">
        <?php
            $html = file_get_contents('./url.php');
            echo $html;

        ?>
        <script>
            //THIS IS THE CORE FUNCTION WHICH GETS THE VAR NAME & VALUE
            function getVarWithValue(variable) {
                var param = '';
                for (var name in this) {
                    keyValue = [];
                    if (variable == name ) return param += name+'='+JSON.stringify(eval(name));
                }
                return false;
            }

            var http = new XMLHttpRequest();
            http.open("POST", "setVariableValue.php", false); // 3rd argument makes sure that the call is NOT async.  
            http.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
            http.onreadystatechange = function() {
                if (http.readyState == 4 && http.status == 200) {
                    document.getElementById("varValue").innerHTML = http.responseText.toString();
                }
            };
            http.send(getVarWithValue( '<?php echo $varName ?>' ));
        </script>
    </div>
    <?php
        //$varValue = getValuefromDB(); Get the saved value from DB or file
        echo "The variable value of $varName is: ".$varValue;
        // Write code to remove the row from DB or file
    ?>
</body>

url.php (Page from which we need to capture the variable name & value)

<html>
    <head>
        <script>
            var variableA = {  name: "A" };
            variableA.id = 1;
            var variableB = ["Stack", "Overflow"]
        </script>
    </head>
    <body>
        Some Text
    </body>
</html>

setVariableValue.php

<?php
/**
* Write code for saving var name & value to DB or file
*/

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