WordPress: Selectively load plugins' styles/JS only for pages/views that needs them

functions.php

function my_deregister_styles() {
    if (!is_page('Contact')) {
        wp_deregister_style('contact-form-7');
    }
    if (!is_single()) {
        wp_deregister_style('tfg_style');
    }
}
function my_deregister_javascript() {
    if (!is_page('Contact')) {
        wp_deregister_script('contact-form-7');
    }
    if (!is_single()) {
        wp_deregister_script('tfg_script');
    }
}
add_action('wp_print_styles', 'my_deregister_styles', 100);
add_action('wp_print_scripts', 'my_deregister_javascript', 100);