Web Features Summary (Baseline 2023-2026)

This skill summarizes web platform features that achieved Baseline status
(available in all major browsers: Chrome, Firefox, Safari) between January 2023
and early 2026. Use this to ensure recommended APIs are widely available without
polyfills.

High-Impact Modern Features (Quick Reference)

JavaScript & Web APIs

• Array & Collections:
  • toSorted(), toReversed(), toSpliced(), with() (Immutable array
    updates)
  • Object.groupBy(), Map.groupBy() (Data grouping)
  • Set methods: intersection(), union(), difference(),
    symmetricDifference()
• Async & Control Flow:
  • Promise.withResolvers() (External promise resolution)
  • Promise.try() (Wrap sync/async functions in a Promise)
  • AbortSignal.any() (Combine multiple abort signals)
  • Array.fromAsync() (Consume async iterables)
• Utilities:
  • URL.canParse() (Safe URL validation)
  • Intl.Segmenter (Locale-sensitive text segmentation)
  • Intl.DurationFormat (Duration string formatting)
  • RegExp.escape() (Escape special characters in regex strings)
  • Uint8Array methods: toBase64(), fromBase64(), toHex(), fromHex()
  • Iterator helpers: map(), filter(), reduce(), toArray() (on
    iterators)

CSS

• Layout & Scoping:
  • Subgrid: (grid-template-columns: subgrid) Align nested grids to parent
    tracks.
  • Container Queries: (@container) Style based on parent size, not
    viewport.
  • @scope: (@scope (.card) to (.content)) True style scoping without
    BEM/Modules.
  • Nesting: Native CSS nesting (similar to Sass).
• Colors & Theming:
  • light-dark(): native light/dark mode color switching.
  • color-mix(): Mix colors in any space (e.g.,
    color-mix(in srgb, red, blue)).
  • Relative colors: Derive colors from others
    (rgb(from var(--bg) r g b / 50%)).
• Typography & Math:
  • text-wrap: balance (Titles) & text-wrap: pretty (Body text).
  • Math functions: pow(), sqrt(), hypot(), log(), exp(), round(),
    mod(), rem(), abs(), sign().
• UI & Interaction:
  • scrollbar-color / scrollbar-width (Standardized scrollbar styling).
  • @starting-style (Entry animations for display: none elements).
  • view-transitions (Native page/element transitions) &
    active-view-transition.
  • ::details-content (Style the inner content of <details> independently).

HTML & DOM

• Interactivity:
  • popover API (Native overlays/tooltips without z-index wars).
  • <dialog> element (now with requestClose() for safe closing).
  • inert attribute (Disable interaction for parts of the DOM).
• Semantics & Loading:
  • <search> element (Semantic wrapper for search forms).
  • <link rel="modulepreload"> (Preload ES modules).
  • fetchpriority (Hint resource priority to browser).

Chrome-Supported Modern Features (Limited Availability)

These features are usable in modern Chrome/Edge (Chromium) but lack full
cross-browser support. Use with caution and always provide fallbacks.

CSS & UI

• Anchor Positioning: (position-anchor, anchor())
  • Status: Chrome 125+. No Firefox/Safari support.
  • Use Case: Tying tooltips/menus to trigger elements without JS.
  • Interop: Requires polyfill or JS fallback (e.g., Floating UI) for other
    browsers.
• Scroll-Driven Animations: (animation-timeline: scroll())
  • Status: Chrome 115+. No stable Firefox/Safari.
  • Use Case: Parallax effects, reading progress bars linked to scroll
    position.
  • Interop: Graceful degradation (animation just doesn't play).
• @scope:
  • Status: Chrome 118+, Safari 17.4+. Firefox pending.
  • Use Case: True component-level styling isolation.
  • Interop: Use BEM/Modules as fallback for Firefox.
• Container Style Queries: (@container style(...))
  • Status: Chrome 111+. No Firefox/Safari.
  • Use Case: Styling children based on parent's computed values (e.g.,
    color).
  • Interop: Highly experimental.

Web Capabilities (Fugu)

• File System Access API: (window.showOpenFilePicker())
  • Status: Chrome 86+, Safari (Origin Private FS only). Firefox (Origin
    Private FS only).
  • Use Case: Reading/Writing local user files directly.
  • Interop: Progressive enhancement only.
• View Transitions (Cross-Document):
  (@view-transition { navigation: auto; })
  • Status: Chrome 126+. Safari 18+. Firefox pending.
  • Use Case: Morphing animations between multi-page navigations.
  • Interop: Graceful degradation (instant navigation).
  • Web Hardware APIs: Chrome-only. Firefox/Safari unlikely to implement.

Modern Best Practices & Discarded Idioms

Adopt These Idioms

• Immutable Arrays: Use toSorted(), toSpliced(), and with() instead of
  mutation.
• Native Grouping: Use Object.groupBy() instead of reduce() patterns.
• Parent Selectors: Use :has() instead of JS-based class toggling for
  parent state.
• Component-First Responsive: Use @container instead of @media for
  internal component layout.
• Native Overlays: Use <dialog> and popover instead of custom
  modal/tooltip logic.
• Native Nesting: Use CSS nesting directly; reduce reliance on preprocessors
  for basic nesting.

Discard These Patterns

• Mutation-in-place: Stop using sort() or reverse() on original arrays
  when state management is involved.
• Viewport-Only Design: Stop assuming component layout is tied strictly to
  screen size.
• JS-Heavy UI: Stop using JavaScript for focus trapping, z-index management,
  and simple "click-outside" logic that <dialog> and popover handle
  natively.

Procedural Guidance

Verify Feature Availability

1. Check the feature name against the list in
   references/baseline_2023_2026.md.
2. Check references/modern_idioms.md for recommended coding patterns.
3. Verify the "Baseline Status" and date.

Additional Resources

Reference Files

• references/baseline_2023_2026.md - Comprehensive list of 100+ web
  features reaching Baseline status.
• references/modern_idioms.md - Detailed comparison of legacy vs. modern
  coding patterns.

Maintenance

• MAINTENANCE.md - Instructions for updating this skill with the latest
  web-features data.

Source Data

Information derived from the
web-features project.