The Accessibility Tree: The DOM for Assistive Tech
The accessibility tree is the DOM's sibling, built for assistive tech. Browsers derive it from your HTML, exposing each element's name, role (e.g., 'button'), and state (e.g., 'checked') to screen readers.
ARIA Live Regions: Announcing Dynamic Content
ARIA live regions tell screen readers about content that changes without a page reload, like a notification banner. Use `aria-live="polite"` for most updates and `assertive` only for critical alerts.
WAI-ARIA Authoring Practices: The Cookbook for Accessible Components
Think of WAI-ARIA Authoring Practices as the official cookbook for accessible web components. It provides patterns for widgets like tabs or accordions, ensuring they work with assistive tech.
CSS :focus-visible: Smart Focus for Accessibility
:focus-visible is a smart focus ring that only appears when needed, like during keyboard navigation. This lets you style accessible focus indicators for keyboard users without showing an outline on every mouse click.
WAI-ARIA Roles: Semantics for Custom Components
WAI-ARIA roles are job titles for HTML elements, telling assistive tech what a generic `<div>` is meant to be, like a tab or button. Use them for custom UI components that lack a native HTML equivalent.
tabindex: Control Element Focus and Tab Order
The `tabindex` attribute lets you control an element's keyboard focus. Use `tabindex="0"` to make custom components tabbable in document order, or `tabindex="-1"` to make an element focusable only by script, like for a modal.
Build Accessible Animations with `prefers-reduced-motion`
`prefers-reduced-motion` lets you respect a user's system-wide request to minimize animations. Use this CSS media query to replace potentially jarring effects like zooms or parallax with simpler fades, preventing discomfort for users with vestibular disorders.
Semantic HTML: Describe Meaning, Not Just Looks
Semantic HTML uses tags that describe the content's role (e.g., `<article>`), not just its appearance. This helps screen readers and search engines understand your page, improving accessibility and SEO. The footgun is using `<div>` for everything.
ElementInternals: Making Custom Elements Form-Friendly
ElementInternals lets your custom elements act like native form inputs, integrating with validation, submission, and labels. Use it for custom inputs in a design system. The footgun: forgetting to call `setFormValue()` means its state won't be submitted.
Constructable Stylesheets: Share Styles, Not Bloat
Create and share CSS in JavaScript without duplication. Constructable Stylesheets are ideal for theming multiple Shadow DOM components from a single source; updates to the sheet propagate to all consumers. A key footgun: @import rules are ignored.
Storybook: A Workshop for UI Components
Storybook is a workshop for UI components, letting you build and test them in isolation without running your entire app. It's used to develop component libraries, document design systems, and test hard-to-reach states.
CSS ::part(): Style Inside a Web Component's Shadow DOM
The `::part()` pseudo-element lets you style specific elements inside a web component's Shadow DOM. It's a contract allowing consumers to theme designated "parts" of a component without breaking encapsulation. The main footgun: it only styles one level deep.
::slotted(): Style Content Passed into Web Components
The ::slotted() pseudo-element lets a Web Component style external content passed into its slots. It's how a component's internal CSS can style the "light DOM" elements it receives.
CSS :host: Style a Web Component from Within
The :host pseudo-class lets a web component style itself from the inside out. Use it inside a shadow DOM to apply styles to the host custom element, making components self-contained. The key footgun: it only works inside a shadow DOM; it has no effect in.
CustomEvent: Sending Custom Data with Events
CustomEvent lets components communicate without direct coupling by firing custom-named events. It's like a private broadcast system for your app. Use it for a child component to signal a parent, passing data in the `detail` property. Don't forget `detail`!
HTML Slots: Making Web Components Customizable
The `<slot>` element is a placeholder inside a Web Component, letting you inject your own markup. It makes components flexible, like a card with customizable header and body sections. The footgun: content without a `slot` attribute goes to the default slot.
The HTML <template> Element: Inert, Reusable Markup
Think of `<template>` as a blueprint for HTML. It holds markup that's invisible and inactive until you need it, perfect for creating reusable chunks like list items that you can stamp out with JavaScript.
Custom Elements: Create Your Own HTML Tags
Think of Custom Elements as creating your own Lego bricks for the web, defining new HTML tags with custom logic. Use them to build reusable components like a `<product-card>`. Be wary of extending built-in elements, as Safari does not support this.
Design Tokens: Automating UI with a Build Pipeline
Think of design tokens as design decisions stored as data. A build pipeline consumes this data to auto-generate code for multiple platforms, ensuring consistency. The footgun is exposing all raw 'option' tokens instead of curated 'decision' tokens.
W3C Design Tokens: A JSON Standard for Design Systems
The W3C Design Tokens format is a universal translator for your design system's variables. It's a standard JSON structure that lets design tools and codebases speak the same language for colors and spacing.