<?php

/**
 * Plugin Name: Preload test
 */

add_action('wp_head', function(){
    if (is_front_page()){
        echo '<link rel="preload" as="image" href="http://3p2mdh1vwccfgkm7h40n7345-wpengine.netdna-ssl.com/wp-content/uploads/2021/01/%E5%9F%8E%E5%B4%8E%E6%B8%A9%E6%B3%89%E3%83%AD%E3%83%BC%E3%83%95%E3%82%9A%E3%82%A6%E3%82%A7%E3%82%A4_21.jpeg">';
    }
},1);

?>