将if / else窗口宽度子句添加到Wordpress navwalker.php

Question

The goal here is to make a Wordpress boostrap main menu top level item which has sub-items act as a clickable link for devices > 768 px wide and retain the default behavior for small device.

There is the following code in the navwalker.php file around line 83:

// If item has_children add atts to a.
if ( $args->has_children && $depth === 0 ) {
    $atts['href'] = '#';
    $atts['data-toggle'] = 'dropdown';
    $atts['class'] = 'dropdown-toggle';
}

To make the link clickable for normal screens I need to modify the code but then add an else statement so that it retains the default behavior, something like:

// If item has_children add atts to a.
if ( $args->has_children && $depth === 0 ) { 
    if ( $windowwidth < 768) {
        $atts['href'] = '#';
        $atts['data-toggle'] = 'dropdown';
        $atts['class'] = 'dropdown-toggle';
    } else {
        $atts['href'] = ! empty( $item->url ) ? $item->url : ''; 
        //$atts['data-toggle'] = 'dropdown';
        $atts['class'] = 'dropdown-toggle';
    }       
}

The question is how to obtain the $windowwidth, presumably in JavaScript, so that I can use it in a PHP if/else clause.