Web Platform and Browser APIs

Web Platform & Browser APIs

programming-languages hub reference for the browser-side JavaScript platform — the APIs that ship in the browser, not in the ECMAScript language (javascript-nodejs) or in Node. This is the half of “JavaScript” that lives between the language and the framework. Sibling to javascript-nodejs, javascript-runtimes-deno-bun-edge, and frontend-design.

TRIGGER: which browser API to use; DOM/events; the observer family; Fetch/Streams/abort; Web Components & Shadow DOM; Service Workers / offline / PWA; client-storage choice; real-time transports (WebSocket/WebRTC/WebTransport/SSE); View Transitions, Navigation API, WebGPU. SKIP: JS language/runtime semantics → javascript-nodejs; non-Node runtimes → javascript-runtimes-deno-bun-edge; framework rendering (React/Vue/Svelte) → frontend-design / frontend-frameworks (concept-tree gap); CSS & visual design → frontend-design; Chrome-extension MV3 surfaces → chrome-dev.

Map of the platform (by purpose)

Area	Core APIs	Notes
DOM & events	`querySelector`, `EventTarget`, event delegation, `CustomEvent`, capture/bubble, passive listeners	Prefer delegation + `AbortController` to remove listeners in bulk
Networking	`fetch`, `Request`/`Response`, `Headers`, `AbortController`/`AbortSignal`, `ReadableStream`/`WritableStream`/`TransformStream`	Streams enable progressive parse; `AbortSignal.timeout()` for deadlines
Components	Custom Elements, Shadow DOM, `<template>`/`<slot>`, declarative shadow DOM, constructable stylesheets	Framework-agnostic encapsulation; SSR via declarative shadow DOM
Offline / PWA	Service Worker lifecycle, `Cache` API, `fetch` interception, Background Sync, Web App Manifest	SW is event-driven & killable — never assume in-memory state persists (see `chrome-dev` for MV3 parallels)
Client storage	`localStorage`/`sessionStorage`, IndexedDB, Cache API, OPFS (Origin Private File System), Storage quotas	See `dexie-indexeddb-local-first-reviewer` for IndexedDB ergonomics
Observers	`IntersectionObserver`, `ResizeObserver`, `MutationObserver`, `PerformanceObserver`	Replace scroll/resize polling; PerformanceObserver feeds Core Web Vitals
Real-time	`WebSocket`, WebRTC (data + media), WebTransport (HTTP/3), Server-Sent Events (`EventSource`)	WebTransport = low-latency, unreliable-or-reliable streams over HTTP/3; SSE for one-way server push
Compute & security	Web Workers, `SharedArrayBuffer`/`Atomics`, Web Crypto (`crypto.subtle`), `crypto.randomUUID()`, the WASM boundary	Offload CPU to workers; Web Crypto for hashing/signing/encryption — never hand-roll crypto
Media & device	Media Capture (`getUserMedia`), Web Audio, Canvas 2D, WebGL/WebGPU, Geolocation, Permissions, Web Bluetooth/USB/Serial	Capability-gated; check `navigator.permissions`

2026 frontier (confirmed current)

Navigation API → Baseline Newly Available (Jan 2026) — Chrome, Edge, Firefox 147, Safari 26.2. The modern replacement for the History API: single navigate event, intercept + transition, proper SPA routing. Prefer it over history.pushState for new SPAs.
View Transitions API — same-document and cross-document; element-scoped transitions now enable targeted animations without animating the whole page.
WebGPU — in production browsers; 2026 is the consistency/predictability year. Compute + 3D; the successor to WebGL.
HTML-in-Canvas — render real DOM elements into a canvas (WebGL/WebGPU) while staying accessible, searchable, translatable.
Document Picture-in-Picture — always-on-top window with arbitrary HTML (Firefox 151 desktop + Chromium).
Soft Navigations API — brings Core Web Vitals measurement to SPA route changes.
Temporal (language, via javascript-nodejs) lands alongside as the modern date/time layer these APIs increasingly assume.

Selection guidance

One-way server push? SSE (EventSource) — simplest, auto-reconnect. Bidirectional low-latency? WebSocket. Media or P2P? WebRTC. HTTP/3 streams / unreliable datagrams? WebTransport.
Client storage: key/value tiny + sync → localStorage; structured/queryable/large → IndexedDB (via Dexie); HTTP responses → Cache API; real files / SQLite-in-browser → OPFS.
Watching layout/visibility? Use the matching observer, never a scroll/resize polling loop.
Encapsulated, framework-free widget? Custom Element + Shadow DOM.
CPU-heavy work? Web Worker (+ Atomics/SharedArrayBuffer for shared state); push to WASM if numeric.
SPA routing (new)? Navigation API + View Transitions, not history.pushState + manual diffing.

Anti-patterns

Polling scroll/resize/setInterval where an observer exists.
Assuming a Service Worker keeps in-memory state across events — it gets terminated.
Hand-rolling crypto instead of crypto.subtle; using Math.random() for tokens instead of crypto.getRandomValues/randomUUID.
Blocking the main thread with heavy compute instead of a Worker.
New SPA routing on the History API when the Navigation API is now Baseline.
Unbounded fetch with no AbortSignal.timeout() — leaks pending requests.

Sources

“New to the web platform in January / May 2026” — web.dev/blog
“Navigation API Reaches Baseline Newly Available” — InfoQ (May 2026)
“15 updates from Google I/O 2026 (Chrome)” — developer.chrome.com/blog/chrome-at-io26
Microsoft Edge 147-149 web platform release notes — learn.microsoft.com
MDN Web Docs — Web APIs reference (canonical)