Build reusable UI components by giving each one a clear job, a small and familiar API, documented interaction and accessibility behavior, and tests both in isolation and in real pages. Reuse is not just copying a visual style: a component is dependable only when its limits and behavior are clear to the people using it.
Start with a distinct interface responsibility
Look for interface needs that recur, then define the single job a component should do. A button, for example, performs an action; a page-level workflow may combine several buttons, fields, and decisions. Keep that workflow composable around the components rather than burying application-specific logic inside a generic control.
This boundary matters for accessibility as well as maintainability. WCAG 2.2 defines a user interface component as part of content perceived by users as a single control for a distinct function (W3C WCAG 2.2). If a proposed component has several unrelated jobs, split it or make the composition explicit.
Design an API people can predict
Expose only the inputs and behavior consumers need. Prefer names, event patterns, and other conventions familiar in the framework and web platform your team uses. A consumer should be able to tell what a component does and how to control it without learning a private mini-language.
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For Web Components, W3C TAG guidance recommends fitting established platform patterns. Use attributes and properties appropriately for simple configuration; for complex data such as objects, arrays, or streams, provide a JavaScript API rather than squeezing those values into awkward attribute strings (W3C TAG Web Components guidance). Choose based on the component’s actual platform and consumers rather than treating one API shape as universal.
- Keep the public surface focused on meaningful variation, not every internal implementation detail.
- Make states and events understandable to the consumers that compose the component.
- Keep page layout and product-specific workflows outside a generic component unless they are genuinely part of its single responsibility.
Structure styles and enhancements in layers
Separate shared foundations from component styles and optional behavior. A useful architecture can distinguish settings, functions, mixins, base styles, layouts, core component styles, and JavaScript-enhanced components. The W3C Design System is one example: it makes core component styles available separately from an enhanced layer, with different CSS bundles (W3C Design System). This is an example, not a required architecture for every project.
Where it suits the implementation, use data attributes as JavaScript hooks. The W3C Design System prefers them because CSS classes are more likely to be overwritten accidentally. Keep styling selectors and behavior hooks conceptually distinct so a visual redesign is less likely to break interaction code.
Make accessibility behavior part of the contract
Document how the component is used and how it behaves for pointer, keyboard, and assistive technology users. The contract should explain relevant names, roles, states, focus movement, and interaction patterns—not just appearance and props.
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W3C’s WCAG 3.0 material dated September 2026 is a Working Draft, not a final recommendation. It says component libraries should define component use and pointer, keyboard, and assistive technology interactions, and recommends accessibility testing and established platform conventions. Treat this as draft guidance and check its status rather than presenting it as a final normative requirement (W3C WCAG 3.0 Working Draft).
- Specify expected keyboard operation and focus behavior for interactive components.
- Describe accessible names, roles, and state communication where applicable.
- Test the behavior, not only the rendered appearance, using the conventions of the platform and framework.
Document usage, states, and limits
Give consumers concise examples of the intended use, available states, and interaction behavior. Include constraints and explain which concerns belong in a surrounding page or workflow. Good documentation prevents a reusable component from becoming a catch-all simply because its limits were never stated.
Test the component alone and in context
Test the component itself for its API, states, interaction behavior, and accessibility needs. Then put it into realistic pages and test again. Page context can change whether an element is understandable and usable; USWDS advises teams to perform their own user testing at page level to gauge a component’s usability in context (USWDS developer guidance).
- Check the isolated component: verify its documented inputs, states, events, and expected interaction paths.
- Check accessibility behavior: exercise pointer and keyboard use, focus behavior, and assistive technology-relevant names, roles, and states as appropriate.
- Check composed pages: test realistic content, neighboring controls, page hierarchy, and the actual workflow in which the component will appear.
- Revise the boundary or API: if consumers need undocumented workarounds or the component behaves ambiguously in context, simplify or clarify the contract.
Choose an approach that fits the team
When deciding whether to adopt, adapt, or build a component library, compare the practical fit rather than looking for a universal winner.
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- Platform fit: Does it work with your framework and target environments?
- API clarity: Does it follow conventions your developers already understand?
- Accessibility contract: Are interactions documented and testable?
- Layering: Can core styles and optional behavior be separated where that helps your product?
- Context testing: Can the components be tested in the real pages and workflows that use them?
The cited guidance supports these as decision criteria, not a head-to-head ranking of specific libraries.
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