wp_register_sidebar_widget() WP 1.0

The default widget option is 'classname' that can be overridden.

The function can also be used to un-register widgets when $output_callback parameter is an empty string.

Basis of: wp_unregister_sidebar_widget()

Hooks from the function

wp_register_sidebar_widget

Return

Null. Nothing.

Usage

wp_register_sidebar_widget( $id, $name, $output_callback, $options, ...$params );

$id(int/string) (required)

Widget ID.

$name(string) (required)

Widget display title.

$output_callback(callable) (required)

Run when widget is called.

$options(array)

An array of supplementary widget options for the instance.

classname(string)
Class name for the widget's HTML container.
Default: shortened version of the output callback name
description(string)
Widget description for display in the widget administration panel and/or theme.

Default: array()

...$params(mixed) (required)

Optional additional parameters to pass to the callback function when it's called.

Notes

Global. Array. $wp_registered_widgets Uses stored registered widgets.
Global. Array. $wp_registered_widget_controls Stores the registered widget controls (options).
Global. Array. $wp_registered_widget_updates
Global. Array. $_wp_deprecated_widgets_callbacks

Changelog

Since 2.2.0	Introduced.
Since 5.3.0	Formalized the existing and already documented `...$params` parameter by adding it to the function signature.

Code of `wp_register_sidebar_widget() wp register sidebar widget` ^{WP 5.6}

wp-includes/widgets.php

<?php
function wp_register_sidebar_widget( $id, $name, $output_callback, $options = array(), ...$params ) {
	global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_widget_updates, $_wp_deprecated_widgets_callbacks;

	$id = strtolower( $id );

	if ( empty( $output_callback ) ) {
		unset( $wp_registered_widgets[ $id ] );
		return;
	}

	$id_base = _get_widget_id_base( $id );
	if ( in_array( $output_callback, $_wp_deprecated_widgets_callbacks, true ) && ! is_callable( $output_callback ) ) {
		unset( $wp_registered_widget_controls[ $id ] );
		unset( $wp_registered_widget_updates[ $id_base ] );
		return;
	}

	$defaults = array( 'classname' => $output_callback );
	$options  = wp_parse_args( $options, $defaults );
	$widget   = array(
		'name'     => $name,
		'id'       => $id,
		'callback' => $output_callback,
		'params'   => $params,
	);
	$widget   = array_merge( $widget, $options );

	if ( is_callable( $output_callback ) && ( ! isset( $wp_registered_widgets[ $id ] ) || did_action( 'widgets_init' ) ) ) {

		/**
		 * Fires once for each registered widget.
		 *
		 * @since 3.0.0
		 *
		 * @param array $widget An array of default widget arguments.
		 */
		do_action( 'wp_register_sidebar_widget', $widget );
		$wp_registered_widgets[ $id ] = $widget;
	}
}