How to add wysiwyg editor in Wordpress meta box
Here is full code example:
add_action( 'add_meta_boxes', function() { add_meta_box('html_myid_61_section', 'TITLEEEEE', 'my_output_function');});function my_output_function( $post ) { $text= get_post_meta($post, 'SMTH_METANAME' , true ); wp_editor( htmlspecialchars($text), 'mettaabox_ID', $settings = array('textarea_name'=>'MyInputNAME') );}add_action( 'save_post', function($post_id) { if (!empty($_POST['MyInputNAME'])) { $datta=sanitize_text_field($_POST['MyInputNAME']); update_post_meta($post_id, 'SMTH_METANAME', $datta ); }}); P.S. MUST-Recommendation from my experience:
Forget adding custom codes, use Advanced Custom Fields, it's excellent and simplify your life.
http://codex.wordpress.org/Function_Reference/wp_editor was by far the easiest method I found, built into Wordpress since 3.3 (so upgrade ;-) )
But you need to replace presentation with nl2br() function as textarea in custom templates have the toogle JS issue, that removes all your <P> and <br/> tags and therefore all line breaks.