An easily solution to remedy that is to move all the .js files in the footer so they will start to load after all the graphical elements of the website have been loaded. In order to do this, open your theme’s functions.php file an place the following code at the bottom.
remove_action('wp_head', 'wp_print_head_scripts', 9);
remove_action('wp_head', 'wp_enqueue_scripts', 1);
add_action('wp_footer', 'wp_print_scripts', 5);
add_action('wp_footer', 'wp_enqueue_scripts', 5);
add_action('wp_footer', 'wp_print_head_scripts', 5);