Hero full browser screen image. Add #hero to img. enqueue script in functions.php

function.php

//Enqueue 
add_action( 'wp_enqueue_scripts', 'jmg_enqueue_all' );
function jmg_enqueue_all() {
    wp_register_script( 'hero', get_stylesheet_directory_uri().'/js/hero.js');	
		wp_enqueue_script('hero', get_template_directory_uri().'/js/hero.js', array('jquery'), false, true);
	
}

hero.js

jQuery(document).ready(function($){
 // Defining a function to set size for #hero 
    function fullscreen(){
        jQuery('#hero').css({
            width: jQuery(window).width(),
            height: jQuery(window).height()
        });
    }
  
    fullscreen();

  // Run the function in case of window resize
  jQuery(window).resize(function() {
       fullscreen();         
    });

});