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Component Model Strawman: Element Registration: Difference between revisions

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Revision as of 19:47, 26 October 2011

Overview

With the Element Registration. page authors can tell new element names and its behavior to agents.

HTMLRegistrationElement

The HTMLRegistrationElement represents an author-registered element definition.

Here is the simplest example which registeres an element named "x-comment" whose instance implements HTMLElement 


// Imperative API
var element = document.createElement("element");
element.name = "x-comment";
document.head.appendChild(element);
// Shorter form.
HTMLRegistrationElement.register("x-comment");

<!-- Markup API -->
<head>
  <element for="x-comment"></element>
</head>

The create callback

The HTMLRegistrationElement provide a pair of lifecycle callbacks for the element instance creation including the tree construction.

The first callback, create is invoked when an agent need a new element instance of the registered element. create callback should return new element instance which matches the registered element specification. 


// Imperative API
var element = document.createElement("element");
element.name = "x-comment";
element.create = function() { return new HTMLElement("x-comment"); };
document.head.appendChild(element);
// Shorter form.
HTMLRegistrationElement.register("x-comment", function() { ... });

<!-- Markup API -->
<head>
  <element for="x-comment">
    <script>
    this.create = function() { return new HTMLElement("x-comment"); };
    </script>
  </element>
</head>

If the callback function has HTMLElement in its prototype chain, it is invoked as a constructor. Thus following two example has same meaning. 


  <element for="x-comment">
    <script>
    class Comment : HTMLElement {
       ....
    };

    this.create = Comment;
    </script>
  </element>

  <element for="x-comment">
    <script>
    class Comment : HTMLElement {
       ....
    };

    this.create = function() { return new Comment(); };
    </script>
  </element>

If no create callback is given, its default behavior is something like this: 


  <element for="x-comment">
    <script>
    var element = this;
    this.create = function() { return new HTMLElement(element.name); };
    </script>
  </element>

The setup callback

The second lifecycle callback, setup is called after an instance creation. If the instance is created by the agent's tree construction, it will be called as a part of the "close" phase. On setup, the attributes and child elements for the element are already set by the agent. So this callback is useful for building its visual like the shadow tree. 


// Imperative API
var element = document.createElement("element");
...
element.setup = function() { this.shadow = new ShadowRoot(this); ...; };
...

<!-- Markup API -->
<head>
  <element for="x-comment">
    <script>
     ...
     this.setup = function() {
       // "this" points the newly created element instance.
       this.shadow = new ShadowRoot(this); 
       ...;
     };
    </script>
  </element>
</head>

If no setup callback is given by the author, agent invokes the default behavior. It is something like this: 

function defaultSetup() {
  if (this.setup)
    this.setup();
}

IDL

[Callback=AcceptConstructor]
interface HTMLRegistrationCreateCallback {
 HTMLElement create();
}:

[Callback]
interface HTMLRegistrationSetupCallback {
 void setup(HTMLElement);
}:

[Constructor]
interface HTMLRegistrationElement {
  attribute String name;
  attribute HTMLRegistrationCreateCallback create;
  attribute HTMLRegistrationSetupCallback setup;
};
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