delite/Widget

delite/Widget is a mixin used by all widgets. It provides fine grained lifecycle methods, shorthand notation for declaring custom setters, and code to read widget parameters specified as DOMNode attributes.

Lifecycle

Declarative creation:

1. Element upgraded to have all methods and properties of the widget class.
2. preRender() callback executed.
3. render() callback executed. Note though that the root node already exists.
4. postRender() callback.
5. Parameters specified as DOMNode attributes (ex: <d-slider max=10>) are mixed into the widget, thus calling custom setters.
6. attachedCallback() callback.

Programmatic creation is:

1. Element created with widget tag name (ex: <d-slider>), and upgraded to have all methods and properties of the widget class.
2. preRender() callback executed.
3. render() callback executed. Note though that the root node already exists.
4. postRender() callback.
5. Parameters specified programatically (ex: new MyWidget({title: "..."})) are mixed into the widget, thus calling custom setters.
6. attachedCallback() callback.

attachedCallback() will be called automatically, although asynchronously.

There are currently five lifecycle methods which can be extended on the widget:

1. preRender()
2. render()
3. postRender()
4. attachedCallback()
5. detachedCallback()

Note that all of these methods except render() are automatically chained, so you don't need to worry about setting up code to call the superclasses' methods.

Also, note that widget authors don't typically extend render() directly, but rather specify the template property. See the handlebars! documentation for more details.

Placement

Delite widgets are DOM Custom Elements. That means they can be placed and manipulated just like other DOM elements. Any DOM manipulation library should work well with instances of the widgets, but there is a helper function for placing the widget in the DOM named .placeAt(). This function takes one or two arguments. The first argument is node being referenced or the string ID of the node and the second argument is where the widget should be positioned.

// Place as last child of someNode
mywidget.placeAt("someNode");

// Place as third child of someNode
mywidget.placeAt("someNode", 3);

// Place before someNode
mywidget.placeAt("someNode", "before");

Events

Assigning listeners to widget events is accomplished via the .on() method. This method takes two parameters:

• type - The type of event being listened for. (e.g. "click")
• listener - The listener function to be called when the event is detected.

Synthetic events can be emitted on the widget or its sub-nodes via the .emit() function. The function takes two arguments:

• type - The type of the event being emitted. (e.g. "click")
• event - Properties to set on the synthetic event object.

Custom setters

Note that custom setters need to call this._set() to record the new value:

_setLabelAttr: function(val){
    this._set("label", val);    // to notify listeners and record the new value
    this.labelNode.textContent = val;   // update the DOM
}