To get wide adoption, a shared framework for reusable, extensible user interface components should, at its core, define the minimum set of requirements necessary to achieve interoperability. This page looks at the principles in QuickUI that allow it support this goal.

Why create a user interface as reusable UI components?

You have enough things to do — solving the same problems over and over is wasting time. If you’ve finally figured out, say, the perfect CSS that wrestles some HTML element into position in one context, it should be possible to use those same exact lines of code somewhere else without resorting to copy-and-paste. It should be straightforward to code your solution as a reusable user interface component that can be used in multiple places — not only by you, but your team, your organization, and the wider web community if you desire.

Creating a UI component shouldn’t be something special; it should be easy enough to be the normal way you create UI — to be a natural part of the UI design and development process. As you go, the output of your work should end up as components that you can again and again. This not only increases your own productivity, it opens the possibility of true network effects in the web UI community: the work we each do should help everyone else go faster, and thereby speed up the rate at which we can all create great user experiences.

There are a variety of ways to create reusable UI components, but many are not extensible. How many times have you found a plugin or widget that did almost — but not quite — what you wanted? Most components aren’t built to be extensible. While their framework may support extensibility, it doesn’t make that easy enough to be the normal course of things.

The QuickUI framework’s entire reason for existence is to create reusable, extensible user interface components. The framework itself makes this the normal course of events.

Core principles

QuickUI has the following core principles:

  1. A control should be as self-contained and context-independent as possible.
  2. A control’s behavior is defined with a regular JavaScript class.
  3. A control’s class can be subclassed.
  4. A control instance is a jQuery instance.
  5. A control instance can host other elements, including additional controls.
  6. A control class can render control instances into the DOM.
  7. A control instance and its top-level DOM element can refer to each other.
  8. A control instance’s properties are read and manipulated with getter/setter functions.

Let’s look at each of these principles in turn.

1. A control should be as self-contained and context-independent as possible

A control shouldn’t need to know anything about its host components (the elements it sits within). If a control can perform some operation inside one element, it should be able to deliver the same functionality inside another element. You shouldn’t have to specially configure the host with styles, contents, event handlers, and so on, just to get the control to work.

A corollary of being context-independent is that the addition of a control to the page should generally not have unexpected effects on other elements on the page. For example, the CSS that defines a control’s visual appearance should, to the degree possible with today’s browsers, only affect instances of that control class. The styles should not inadvertently be picked up by other elements on the page.

You should be able to add a control to a page anywhere without breaking or otherwise effecting other aspects of that page. For that matter, you should generally be able to add multiple instances of a control to a page, and everything should still work.

2. A control’s behavior is defined with a regular JavaScript class

If you’re a JavaScript developer, you already use JavaScript’s native class support to define reusable behavior. In QuickUI, when you’re creating a new kind of control, you’re creating a JavaScript class. You can define control behavior through instance methods and class methods as regular JavaScript functions. Everything about working with controls is the same as working with classes: e.g., you can test whether an instance of a control class is a member of class with the standard “instanceof” keyword.

3. A control’s class can be subclassed

You can create a control class that inherits from another control using a standard prototype-based inheritance scheme. This means that all the behavior of the superclass (also known as the base class) is available to your subclass. Rather than creating a new inheritance scheme, QuickUI uses the inheritance system built into jQuery. All QuickUI controls inherit from a base Control class, which in turn inherits from the base jQuery class.

4. A control class instance is a jQuery instance

Because all control classes ultimately derive from the base jQuery class, all QuickUI control instances are also jQuery instances. You can show and hide control instances with $.show() and $.hide(), you can manipulate a control’s CSS styling with $.css(), you can animate a control with $.animate(), and so on.

5. A control instance can host other elements, including additional controls

Controls are typically nestable. Control classes can be designed so that you can place additional elements, either plain HTML or other controls, inside a given control instance. Whether and where a control allows nested elements is up to the control class.

Following the principle of context-independence (above), a control class should generally be able to contain and cope with arbitrary contents. So if you find or create, say, a certain kind of tabbed UI control, you should be able to place whatever content you want inside a tab, and you should be able to put that tabbed UI inside other controls.

6. A control class can render instances as complete DOM subtrees

When you create a control class, your class can define a render function: a function which will be invoked when a new instance of your control class is being created. This render function creates the DOM elements that comprise the control’s initial structure.

This means that control classes can be instantiated without depending upon placeholder elements having been previously entered into the DOM. In some control frameworks, it’s a requirement that certain HTML elements be created first, before a user interface component can be created; the component relies on those elements, manipulating and adding to them as it sees fit. Unfortunately, this technique creates brittle dependencies on your control class’ definition. If you decide that your control should be constituted with a different set of HTML elements, all existing hosts of that control class will have to be updated to match. In contrast, a QuickUI control class can render all the elements it needs itself. You can change your class’ definition later without fear of breaking all existing uses of that class.

When a control instance is rendered, a top-level DOM element is created (usually a div, but a control class can ask for a different top-level element). This element becomes the top of a DOM subtree containing all elements of the control. Which elements get added to that subtree is determined by your control class’ hierarchy. Each class in the hierarchy, from the base Control class, and moving down to your specific control class, gets a chance to render DOM elements into the subtree. The subtree can then be added to the page DOM, or saved for use later.

What this means is that QuickUI control classes have a rigorously-defined relationship to their parent classes and subclasses. Your control class can rely upon its parent classes having already added their elements to the DOM subtree. Your class can then add its own elements to the subtree, nesting those within the elements that are guaranteed to be there. Finally, your class can give its own subclasses a chance to add their nested elements to the subtree.

7. A control instance and its top-level DOM element can refer to each other

As mentioned above, a control instance is a jQuery instance. The value of that jQuery instance is an array of one or more elements that point to DOM subtrees which have been rendered by the control class. In other words, when you have a reference to a logical control object, you inherently have access to the DOM elements that visually represent that control.

Conversely, the visual DOM subtree rendered by a control instance retains a persistent reference pointing back to the logical control instance. This allows you to obtain a reference to a DOM element, for example, using jQuery selectors, and then get back the control instance that originally created that DOM element. This control reference is automatically cast back to the correct JavaScript class for you; you don’t have to remember which class was used to create which elements.

8. A control instance’s properties are read and manipulated with getter/setter functions

When you want to manipulate a control instance, you do so by invoking control instance methods, which are typically defined as jQuery-style getter/setter property functions. Such functions generally take one optional parameter. If the parameter is omitted, the function is being invoked to get the value of that property. If the single parameter is supplied, the function is being invoked to set the value of that property.

Following jQuery convention, the setter form of a property function is chainable, meaning that you can continue applying additional instance functions to it. Also following jQuery convention, the setter form of a property function can manipulate an array of controls in a single call. This makes it easy for you to quickly manipulate collections of similar controls, e.g., all the controls in a list.