It looks like your condition check is correct. As per the comments to the question, don’t forget to add it as a callback to the wp_enqueue_scripts action hook.
function enqueue_styles_and_scripts() {
if ( is_page_template('htmlcode.php') ) {
wp_enqueue_style( 'code-mirror-css', get_template_directory_uri() . '/code-mirror/plugin/codemirror/lib/codemirror.css', array(), 'all');
wp_enqueue_style( 'code-mirror-monokai', get_template_directory_uri() . '/code-mirror/plugin/codemirror/theme/monokai.css', array(), 'all');
wp_enqueue_script( 'code-mirror-js', get_template_directory_uri() . '/code-mirror/plugin/codemirror/lib/codemirror.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirror-addon', get_template_directory_uri() . '/code-mirror/plugin/codemirror/addon/selection/selection-pointer.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirror-mode-xml', get_template_directory_uri() . '/code-mirror/plugin/codemirror/mode/xml/xml.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirrror-mode-javascript', get_template_directory_uri() . '/code-mirror/plugin/codemirror/mode/javascript/javascript.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirrror-mode-css', get_template_directory_uri() . '/code-mirror/plugin/codemirror/mode/css/css.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirrror-mode-vbscript', get_template_directory_uri() . '/code-mirror/plugin/codemirror/mode/vbscript/vbscript.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirrror-mode-htmlmixed', get_template_directory_uri() . '/code-mirror/plugin/codemirror/mode/htmlmixed/htmlmixed.js', array(), '1.0.0', true );
wp_enqueue_script( 'code-mirrror-config', get_template_directory_uri() . '/code-mirror/js/config.js', array(), '1.0.0', true );
}
}
add_action( 'wp_enqueue_scripts', 'enqueue_styles_and_scripts' );