You can use Dojo widgets, or "dijits", to add prepackaged user interface components to your applications. Dojo has many existing dijits you can choose from such as text boxes, buttons, menus, calendars, color pickers, and so on.
Dijits have been tested to behave consistently in different browsers and comply with accessibility and localization requirements. The dijit framework is extensible, so with a little ambition you can even create your own dijits.
You can also combine several dijits into one for easy re-use. Suppose your company has multiple Web designers that want to embed maps in their pages. You can wrap up a map and some other elements inside a dijit, which the Web designers can then add to their pages without having to learn how to use the ArcGIS JavaScript API.
Dijits can also help users accomplish focused workflows, such as finding nearby dentists, selecting a site for a business, or generating a route. In this way, dijits are similar to "tasks" in the Web ADF.
If you have dijits that appear in your page when the application loads, you should include this line before adding the script tag that references the ArcGIS JavaScript API:
<script>var dojoConfig = { parseOnLoad: true }</script>