wordpress - how to add WYSIWYG to textarea with a specific class
It depends on where your textarea is located - options page, settings page, meta box?
Say that it's located in an options page, and you have saved option called my_option. First you'd fetch that option:
$my_option = get_option( 'my_option' );And then you'd call the editor
wp_editor( $my_option , 'my_option', array( 'wpautop' => true, 'media_buttons' => false, 'textarea_name' => 'my_option', 'editor_class' => 'my_custom_class', 'textarea_rows' => 10) );This should display the TinyMCE editor in your textarea.
Check out the codex for wp_editor to see what other arguments you can set.
In case of post or page metabox, you'd save the options in a meta field and get them out with get_post_meta() function.