Hooks to trigger a callback when adding, removing, rearranging or updating a widget in the widget area

I ended up using the updated_option hook and checking if a widget or sidebar has been updated.

When a widget is added, removed or saved, the update_option hook is fired.

All widget option names start with “widget_“. By checking if the option name starts with “widget_” we can determine if a widget was added, removed or saved.

When widgets are being reordered within a widget area, the new positions are being saved to the option sidebars_widgets.

The hook updated_option fires immediately after an option has been successfully updated. Note: updated_option will not fire if the old value and the new value are the same.

function purge_cache_on_widget_change( $option, $old_value, $value ) {
    if( substr( $option, 0, 7 ) === 'widget_' || $option === 'sidebars_widgets' ) {
add_action('updated_option','purge_cache_on_widget_change', 10, 3);