将javascript值分配给php变量

我正在尝试检查屏幕宽度并将其分配给php变量以执行一些if else语句。这就是我得到的。

I'm trying to check screen width and assign it to a php variable to do some if else statements. This is what I got.

<script>
    var mobileFormWidthCheck = $(window).width();
    var mobileFormReady;
    if(mobileFormWidthCheck < 767){
        mobileFormReady = 22;
    }
    else{
        mobileFormReady = 55;  
    }

</script>

    <?php   
        $widthChecked = "<script>document.write(mobileFormReady);</script>";
        echo $widthChecked;
    ?>

这完美无缺。但是，当我尝试基于 mobileFormReady 值回显某些内容时，它不会回显。

This works perfectly. But when I try to echo something based on the mobileFormReady value, it doesnt echo.

这就是我试图开始工作的原因。

This is what im trying to get to work.

$widthChecked = "<script>document.write(mobileFormReady);</script>";
if($widthChecked == "22"){
  echo 'this page is under 767 pixels';
}
else if($widthChecked == "55"){
  echo 'this page is OVER 767 pixels';
}
else{
  echo 'NOT WORKING YET';
}

我认为这是一个字符串整数问题。但我似乎无法弄明白。你能帮我吗？非常感谢。

I think its a string integer issue. But I cant seem to figure it out. Can you guys please help me? Thanks a lot.