# A tour of how the Widget (Virtual DOM) code in Discourse works

**URL:** https://meta.discourse.org/t/a-tour-of-how-the-widget-virtual-dom-code-in-discourse-works/40347
**Category:** Development
**Created:** [29 februari 2016 om 20:18 UTC](https://meta.discourse.org/t/a-tour-of-how-the-widget-virtual-dom-code-in-discourse-works/40347 "2016-02-29T20:18:39Z")
**Posts on this page:** 1
**Showing post:** 57

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### Author: ![eviltrout](https://sea3.discourse-cdn.com/meta/user_avatar/meta.discourse.org/eviltrout/32/5275_2.png) [@eviltrout](https://meta.discourse.org/u/eviltrout)
#### Post date: [4 september 2017 om 15:12 UTC](https://meta.discourse.org/t/a-tour-of-how-the-widget-virtual-dom-code-in-discourse-works/40347/57 "2017-09-04T15:12:16Z")

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Thanks for pointing out that the core widget is watching for an app event in `defaultState` - that is actually incorrect as it is never unloaded (cc @tgxworld) . In the case of search that might not be a problem since the widget is probably never unmounted but it’s not correct. (I’ve added it to my list to improve.)

The correct way to delegate events to widgets is by using `dispatch()`. For example:

[https://github.com/discourse/discourse/blob/master/app/assets/javascripts/discourse/components/site-header.js.es6#L63](https://github.com/discourse/discourse/blob/master/app/assets/javascripts/discourse/components/site-header.js.es6#L63)

In that case, every time the `notifications:changed` event is fired, it will call `notificationsChanged()` in the `user-notifications` widget. After the method is called, it will automatically queue a rerender.

The event will be automatically removed when the widget is unmounted.

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