is_customize_preview()

Whether the site is being previewed in the Customizer.

Return

(bool) True if the site is being previewed in the Customizer, false otherwise.

function is_customize_preview() {
	global $wp_customize;

	return ( $wp_customize instanceof WP_Customize_Manager ) && $wp_customize->is_preview();
}

Used By
Used By	Description
wp-includes/customize/class-wp-customize-selective-refresh.php: WP_Customize_Selective_Refresh::handle_render_partials_request()	Handles the Ajax request to return the rendered partials for the requested placements.
wp-includes/general-template.php: wp_site_icon()	Display site icon meta tags.
wp-includes/general-template.php: get_custom_logo()	Returns a custom logo, linked to home.
wp-includes/widgets/class-wp-widget-text.php: WP_Widget_Text::render_control_template_scripts()	Render form template scripts.
wp-includes/widgets/class-wp-widget-recent-comments.php: WP_Widget_Recent_Comments::__construct()	Sets up a new Recent Comments widget instance.
wp-includes/nav-menu-template.php: _wp_menu_item_classes_by_context()	Add the class property classes for the current context, if applicable.
wp-includes/admin-bar.php: wp_admin_bar_customize_menu()	Adds the “Customize” link to the Toolbar.
wp-includes/theme.php: _custom_background_cb()	Default custom background callback.
wp-includes/theme.php: wp_custom_css_cb()	Render the Custom CSS style element.
wp-includes/theme.php: get_custom_header_markup()	Retrieve the markup for a custom header.
wp-includes/theme.php: the_custom_header_markup()	Print the markup for a custom header.

Changelog
Version	Description
WP-4.0.0	Introduced.