PHP string to integer conversion not working with this code

Question

All things going right until converting a string to an integer. After converting, the value becomes 0. Why?

<script type="text/javascript">
    var offset = new Date().getTimezoneOffset(); //get client timezone differance with UTC
    offset *= -1; // change sign
    offset *= 60; // convert into second
    console.log(offset);
</script>

<?php 
    echo "<br/><br/>";
    $a = "<script>document.write(offset)</script>"; //getting value in string
    echo $a; // this works and print : 19800
    echo "<br/>"; 
    settype($a, "integer");
    echo $a; // print 0
?>

PHP executes before your javascript, right now its setting the type $a with the string inside it, not the offset that you want to, and why not just use the javascript way of setting the type? — Kevin
– Kevin, Commented Feb 22, 2018 at 7:17
I tried setting integer type in javascript also but when I store a value in PHP variable $a, It is changed into a string. — Leet Hudka
– Leet Hudka, Commented Feb 22, 2018 at 7:27
I think you're confused on how PHP and javascript works, under the context of PHP the value of $a is still "<script>document.write(offset)</script>";, when it its rendered into the page (since you echoed the script tags), now the JS kicks in, in turn showing you the illusion that the value is 19800, so no $a is not actually 19800 — Kevin
– Kevin, Commented Feb 22, 2018 at 7:33
Your $a variable is indeed a string, when page is loaded javascript executed and outputs (by document.write) previousy calculated offset. — Alexey Chuhrov
– Alexey Chuhrov, Commented Feb 22, 2018 at 7:35
Then what should I do to store 19800 instead of "<script>document.write(offset)</script>"; — Leet Hudka
– Leet Hudka, Commented Feb 22, 2018 at 7:36

Sebastian Brosch · Accepted Answer · 2018-02-22 07:48:56Z

2

You set some HTML (with JavaScript) code in variable $a. This is not a valid number! So PHP can't convert the not numeric string into a number / integer:

$a = "<script></script>";
var_dump($a); //string(17) "<script></script>"
settype($a, "integer");
var_dump($a); //int(0)

The code is working if you set a numeric value as string (or integer) on the $a:

$a = "19800";
var_dump($a); //string(5) "19800"
settype($a, "integer");
var_dump($a); //int(19800)

Note: You can't directly assign the result from JavaScript to a PHP variable because the JavaScript code is executed on client side and PHP is executed on server side (before JavaScript). You can use AJAX to send values from JavaScript back to the server to use them on server side too.

edited Feb 22, 2018 at 7:48

answered Feb 22, 2018 at 7:41

Sebastian Brosch

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