How can i convert the PHP string into an integer, but php string is fetched from javascript written in the same page?

Question

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>if else in php</title>
</head>

<body>

    <script>
        var a = 123;
        //to send the prompt value to php, reference taken from stack overflow
    </script>
    <?php
    $a = "<script>document.writeln(a)</script>";
    echo $a;
    ?>
</body>

</html>

in the code above, i fetched the value of javascript variable 'a' in PHP i successfully get it in the variable $a and i tried to print it then also it got printed successfully. As $a would be containing number '123' in string i tried to convert it into an integer using intval() function but, it always shows me value of $a as 0 when i echo it. the below code describes the same

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>if else in php</title>
</head>

<body>

    <script>
        var a = 123;
        //to send the prompt value to php, reference taken from stack overflow
    </script>
    <?php
    $a = "<script>document.writeln(a)</script>";
    $a = intval($a);
    echo $a;
    ?>
</body>

</html>

Your hole implementation is wrong. PHP and JavaScript do not share variables between each other, and please be more specific. what do you want to do exactly with it? — John
– John, Commented Dec 26, 2021 at 17:18
Actually i was learning php so even though php is server side scripting language, i wanted to take input from javascript and have to use it in php. by the way i was just learning if elseif ladder in php so i just wanted input from user and depending upon that input i wantto tell him if he can drive a car or not. — Vidhanshu borade
– Vidhanshu borade, Commented Dec 26, 2021 at 17:27
Php executes before JavaScript. The whole approach makes no sense, and the example is so confected and oversimplified it's impossible to tell what your real purpose is — ADyson
– ADyson, Commented Dec 26, 2021 at 17:32
If you want to take a variable from the browser and send it to a php script you need to send it via a http request - e.g. sending via Ajax, or via submitting a form — ADyson
– ADyson, Commented Dec 26, 2021 at 17:33
yes that's what i want to do but i was not knowing any other way for doing this, asa beginner in php i tried to use javascript variable value in php. — Vidhanshu borade
– Vidhanshu borade, Commented Dec 26, 2021 at 17:37

John · Accepted Answer · 2021-12-26 17:37:54Z

You have to submit it to the server to process it. Here a working example.

<?php

$canDrive = false;

// use GET to retrieve the value of the "age" query string

if(isset($_GET["age"]) && $_GET["age"] >= 18) $canDrive = true;



?>


<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>if else in php</title>
</head>

<body>

    <!-- Here goes your code   -->
    <?php
    if ($canDrive) {
        echo "You can drive";
    } else {
        echo "You can't drive";
    }
    ?>


<form action="" method="get">
        <input type="text" name="age" id="">
        <input type="submit" value="submit">
    </form>

</body>

</html>

Remember, JavaScript and PHP can't communicate directly.

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How can i convert the PHP string into an integer, but php string is fetched from javascript written in the same page?

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