AJAX In Action [61]
This concludes our brief review of cross-browser libraries. Our choice of libraries has been somewhat arbitrary and incomplete. As we have noted, there is a lot of activity in this space at the moment, and we’ve had to limit ourselves to some of the more popular or well-established offerings. In the next section, we’ll look at some of the widget frameworks built on top of these and other libraries. 3.5.2 Widgets and widget suites
The libraries that we’ve discussed so far have provided cross-browser support for some fairly low-level functionality, such as manipulating DOM elements and fetching resources from the server. With these tools at our disposal, constructing functional UIs and application logic is certainly simplified, but we still need to do a lot more work than our counterparts working with Swing, MFC, or Qt, for example. Prebuilt widgets, and even complete widget sets for Ajax developers, are starting to emerge. In this section, we’ll look at a few of these—again, more to give a flavor of what’s out there than to provide a comprehensive overview. Scriptaculous
The Scriptaculous libraries are UI components built on top of Prototype (see the previous section). In its current form, Scriptaculous provides two major pieces of functionality, although it is being actively developed, with several other features planned. The Effects library defines a range of animated visual effects that can be applied to DOM elements, to make them change size, position, and transparency. Effects can be easily combined, and a number of predefined secondary effects are provided, such as Puff(), which makes an element grow larger and more transparent until it fades away completely. Another useful core effect, called Parallel(), is provided to enable simultaneous execution of multiple effects. Effects can be a useful way of quickly adding visual feedback to an Ajax user interface, as we’ll see in chapter 6.
Invoking a predetermined effect is as simple as calling its constructor, passing in the target DOM element or its ID as an argument, for example:
Licensed to jonathan zheng Third-party libraries and frameworks 109 new Effect.SlideDown(myDOMElement); Underlying the effects is the concept of a transition object, which can be parameterized in terms of duration and event handlers to be invoked when the transition ends. Several base transition types, such as linear, sinusoidal, wobble, and pulse, are provided. Creating a custom effect is simply a matter of combining core effects and passing in suitable parameters. A detailed discussion of building custom effects is beyond the scope of this brief overview. We’ll see Scriptaculous effects in use again in chapter 6, when we develop a notifications system. The second feature that Scriptaculous provides is a drag-and-drop library, through the Sortable class. This class takes a parent DOM element as an argument and enables drag-and-drop functionality for all its children. Options passed in to the constructor can specify callback handlers for when the item is dragged and dropped, types of child elements to be made draggable, and a list of valid drop targets (that is, elements that will accept the dragged item if the user lets go of it while mousing over them). Effect objects may also be passed in as options, to be executed when the item is first dragged, while it is in transit, and when it is dropped. Rico Rico, like Scriptaculous, is based on the Prototype library, and it also provides some highly customizable effects and drag-and-drop functionality. In addition, it provides a concept of a Behavior object, a piece of code that can be applied to part of a DOM tree to add interactive functionality to it. A few example Behaviors are provided, such as an Accordion widget, which nests a set of DOM elements within a given space, expanding one at a time. (This style of widget