Dissecting Dijit: Dojo Widgets

Category: Articles , Component , Dojo

One of the best parts of Dojo 1.0 has been how often the team has been blogging of all things. It has been great!

Mike Wilcox has posted about Dijit, the widget platform for Dojo 1.0.

His piece covers dojo.parser, dojo.declare, the widget markup, the lifecycle of widgets, and more. Great stuff.

The lifecycle is very thorough:

preamble(): Originating in dojo.declare, preamble is a new Dojo Core feature. Itâ€™s a pre-constructor accessory. By analogy, preamble is to constructor as postMixInProperties is to postCreate. Since preamble gets the same arguments as the constructor, you may extend another object, and jump in front of the constructor and change the arguments.
constructor(): Originating in dojo.declare, constructor has a new usage pattern. Previously, it fired last, which I didnâ€™t find particularly useful nor accurate. It now fires early in the widget lifecycle, allowing early initialization with the arguments passed into the object. While more common in use, itâ€™s not exactly necessary, as Dijit handles the job of converting your arguments into object properties.
postMixInProperties(): Originating in dijit._Widget, postMixInProperties is used more commonly by widget developers. That said, some of its duties are superseded by the addition of constructor and preamble. Its main purpose is firing after the properties have been set, but before the widget has been parsed and created. Pre-creation work on widget properties is typically done in this method.
postCreate(): Originating in dijit._Widget, postCreate is the â€œheavy lifterâ€ of Dijit. This fires after creation, but before the widget is rendered to the page. At this time in the widget lifecycle, you have access to the widgetâ€™s nodes, so additional parsing, connections, styling, or even attaching more widgets is possible.
startup(): Originating in dijit._Widget, startup is somewhat misunderstood. startup doesnâ€™t fire unless the widget is a child of another widget. And then it only fires after it, and all of its siblings have been created. Then they all fire together.