window.innerWidth JavaScript Value in PHP

Question

I'm wanting to set a PHP variable based on window.innerWidth.

For testing purposes, I have my browser at full size and document.write(window.innerWidth); returns 1920, which seems to be right.

However, the code below is always returning "small" for the PHP variable $window_size.

<script>
 if(window.innerWidth > 1000){
    <?php $window_size = 'big'; ?>
 } else {
    <?php $window_size = 'small'; ?>
 }
</script>

Any ideas?

can't do it that way, PHP is processed on the server, not in the browser — SoluableNonagon, Dec 23 '15 at 19:20
Here's a hint: what's the purpose of php? what does php generate? — Amit, Dec 23 '15 at 19:21
Related: [Use a DIV's width in If statement in Php file](https://stackoverflow.com/questions/34275759/use-a-divs-width-in-if-statement-in-php-file/34276094) — Cave Johnson, Dec 23 '15 at 19:28
If your IF statement true than how small value set every time? — devpro, Dec 23 '15 at 19:50

SoluableNonagon · Answer 1 · 2015-12-23T19:31:48.323

-1

You can't determine the window size this way on the back end, the JS would need to send this data at some point to the back end for it to know the window size.

<script>
 var windowSize;
 if(window.innerWidth > 1000){
    windowSize = 'big';
 } else {
    windowSize = 'small';
 }
 $.ajax({ url: 'some/back/end', data: windowSize }); // send to server.
</script>

This is because PHP, your backend, generates HTML. So your Browser then gets the HTML (with JS in it) and then runs it. By that point, those PHP statements were already executed and the server doesn't know about them.

So your PHP script is executed and does the following

<?php $window_size = 'big'; ?>
<?php $window_size = 'small'; ?>

It ignores the if because it is not a PHP if statement, and so the value of $window_size is always small

edited Dec 23 '15 at 19:31

answered Dec 23 '15 at 19:23

SoluableNonagon

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Well, whoever downvoted, please explain why. – SoluableNonagon Dec 23 '15 at 19:26
If you want the PHP to be aware of the window size, then the only way is for JS to send that info to the server. This way, the server can save the variable and use it later. – SoluableNonagon Dec 23 '15 at 19:28
This was likely down voted because you answered a _very_ common question (this making it a duplicate) instead of flagging it. – Kevin Brown-Silva Dec 24 '15 at 03:47

window.innerWidth JavaScript Value in PHP

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