Run JS only on pages with my widget - php

Question

I'm trying to get a widget to only load javascript on a page where the widget is present.
I've tried adding the add action in the 'showWidget' didn't work.
What am I doing wrong?
PHP
wp_register_sidebar_widget('MyWidget','MyWidget', 'showWidget');
add_action('wp_enqueue_scripts', 'addScript'); //now the script appears on every page
function addScript()
{
wp_register_script('MyWidgetJs', plugins_url( '/script.js' , __FILE__), array('jquery'));
wp_enqueue_script('MyWidgetJs');
}
function showWidget($args)
{
// add_action('wp_enqueue_scripts', 'addScript'); //I tried this but it doesn't work :(
wp_enqueue_script('MyWidgetJs');
extract($args);
/* do widget stuff */
}

Answer 1

Seems that the new version of WordPress supports this: http://codex.wordpress.org/Version_3.3
Register your script, but don't enqueue it. In your widget PHP, add in the wp_enqueue_script('your_script_name'); and it'll load it only when your widget is used and place it in the footer.
You are going to upgrade to 3.3, right? :)
SO, something like this should work just fine:
wp_register_sidebar_widget('MyWidget','MyWidget', 'showWidget');
function showWidget($args) {
wp_enqueue_script('MyWidgetJs');
extract($args);
/* do widget stuff */
}

Answer 2

You want to use is_active_widget() conditional to do something like:
<?php
if ( is_active_widget('MyWidget') ) {
add_action('wp_enqueue_scripts', 'addScript');
}
?>
using your above code the final widget may look like:
<?php
if ( is_active_widget('MyWidget') ) {
add_action('wp_enqueue_scripts', 'addScript');
}
function addScript()
{
wp_register_script('MyWidgetJs', plugins_url( '/script.js' , __FILE__), array('jquery'));
wp_enqueue_script('MyWidgetJs');
}
function showWidget($args)
{
wp_enqueue_script('MyWidgetJs');
extract($args);
/* do widget stuff */
}