how to load css and js based on post template

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' );