WordPress at a glance
function is not described

WP_Customize_Nav_Menu_Setting::preview() public WP 4.3.0

Handle previewing the setting.

{} It's a method of the class: WP_Customize_Nav_Menu_Setting{}

No Hooks.

Return

true|false. False if method short-circuited due to no-op.

Usage

$WP_Customize_Nav_Menu_Setting = new WP_Customize_Nav_Menu_Setting();
$WP_Customize_Nav_Menu_Setting->preview();

Notes

Changelog

Since 4.3.0 Introduced.
Since 4.4.0 Added boolean return value

Code of WP_Customize_Nav_Menu_Setting::preview() WP 5.7.2

<?php
public function preview() {
	if ( $this->is_previewed ) {
		return false;
	}

	$undefined      = new stdClass();
	$is_placeholder = ( $this->term_id < 0 );
	$is_dirty       = ( $undefined !== $this->post_value( $undefined ) );
	if ( ! $is_placeholder && ! $is_dirty ) {
		return false;
	}

	$this->is_previewed       = true;
	$this->_original_value    = $this->value();
	$this->_previewed_blog_id = get_current_blog_id();

	add_filter( 'wp_get_nav_menus', array( $this, 'filter_wp_get_nav_menus' ), 10, 2 );
	add_filter( 'wp_get_nav_menu_object', array( $this, 'filter_wp_get_nav_menu_object' ), 10, 2 );
	add_filter( 'default_option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );
	add_filter( 'option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );

	return true;
}