I use WordPress 5.2.2 and I develop a custom theme.

EDIT : On my theme I added a metabox who show an input type=”text”.

Code in functions.php of my theme

if ( ! function_exists( 'vn_add_metabox' ) ) {
    function vn_add_metabox () {
        add_meta_box('vn_youtube_single_metabox', __('Youtube link', WP_THEME_TEXTDOMAIN), 'show_vn_youtube_link_metabox', array('post', 'page'), 'side', 'low');

    }
    add_action( 'add_meta_boxes', 'vn_add_metabox' );
}

This metabox call show_vn_youtube_link_metabox who display an input text and youtube video iframe

if (!function_exists('show_vn_youtube_link_metabox')) {
    function show_vn_youtube_link_metabox()
    {
        global $post;
        show_vn_input_text('vn_youtube_link'); // <input type="text" name ="vn_youtube_link" value="VALUE_POST_META" />
        echo '<br/>'.vn_get_youtube_iframe(get_post_meta( $post->ID, 'vn_youtube_link', true )); /*<iframe class="youtube-video-iframe" src="'.VIDEO_LINK.'?rel=0" width="790" height="496" allowtransparency="true" style="width:100%;" frameborder="0" allowFullScreen allow="encrypted-media" ></iframe> */
    }
}

I save value of postmeta on action save_post

if ( ! function_exists( 'vn_save_metabox_value' ) ) {
    function vn_save_metabox_value ( $post_id, $post ) { // Enregistrement des données dans la base WordPress.
        //évite de perdre des données à cause de l'enregistrement automatique
        if ( ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) || ( defined( 'DOING_AJAX' ) && DOING_AJAX ) || isset( $_REQUEST[ 'bulk_edit' ] ) ) {
            return $post->ID;
        }
        // Vérification des droits de l'utilisateur.
        if ( ! current_user_can( 'edit_post', $post->ID ) ) {
            return $post->ID;
        }

        vn_save_meta_box_content($post, 'vn_youtube_link');

        return $post->ID;
    }

    add_action( 'save_post', 'vn_save_metabox_value', 1, 2 );
}

I use a function to control value of postmeta and save it

if ( ! function_exists( 'vn_save_meta_box_content' ) ) {
    function vn_save_meta_box_content ( $post, $meta_box_id, $input_name = '' ) {
        if ( ! isset( $input_name ) || empty( $input_name ) ) {
            $input_name = $meta_box_id;
        }

        if ( ! isset( $_POST[ $input_name ] ) || empty( $_POST[ $input_name ] ) ) {
            delete_post_meta( $post->ID, $meta_box_id );
        } else {
            if ( get_post_meta( $post->ID, $meta_box_id, true ) ) {
                update_post_meta( $post->ID, $meta_box_id, $_POST[ $input_name ] );
            } else {
                add_post_meta( $post->ID, $meta_box_id, $_POST[ $input_name ] );
            }
        }
    }
}

I want to execute a JS function (AJAX or other) after the AJAX done by WordPress to update post (XHR POST http://localhost/wp_uimm/wp-json/wp/v2/pages/5?_locale=user) on admin post edit screen. This javascript function will be used to display the iframe or link of the youtube video without refreshing the post edit screen.

Is there a callback to execute a function when wp POST has done ?

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