HTML5 APIs Overview

"HTML5" is often used loosely to mean not just new markup elements, but the whole wave of browser JavaScript APIs that shipped alongside them — letting pages do things that used to require plugins like Flash: draw graphics, store data locally, know the user's location, and more. This page is a map of that territory, with links to the dedicated pages on this site where one exists.

APIs Covered in Depth Elsewhere on This Site

API	What it does	Dedicated page
Web Storage	Simple key-value persistence per origin, in the browser	`web-storage`
Geolocation	Ask the user for their physical location	`geolocation`
Drag and Drop	Native pick-up-and-drop interactions for elements and files	`drag-and-drop`
Canvas	Immediate-mode 2D (and 3D via WebGL) pixel drawing surface	`canvas-basics`
Web Components (Custom Elements, Shadow DOM, `<template>`, `<slot>`)	Build reusable, encapsulated custom tags	`custom-elements`, `shadow-dom`, `template-element`, `slot-element`
contenteditable	Make any element directly user-editable	`contenteditable`
`data-*` attributes	Attach custom data to elements for JS to read	`data-attributes`

Other Notable HTML5-Era APIs

These are not covered as dedicated pages in this HTML section (some belong more naturally under JavaScript or Web APIs topics), but are worth knowing exist:

API	One-line summary
Fetch	Modern, Promise-based replacement for `XMLHttpRequest` — makes HTTP requests from the browser
Notifications	Show native OS-level notifications from a web page, with user permission
Fullscreen	`element.requestFullscreen()` — let a page or a single element take over the whole screen
Clipboard	`navigator.clipboard.writeText()` / `.readText()` — programmatic copy/paste, permission-gated
File API	Read files the user selects or drops, as text, binary, or a data URL
History	`pushState`/`replaceState` — manipulate the browser URL and back/forward stack without a full reload
Web Workers	Run JavaScript on a background thread, off the main UI thread
WebSockets	Persistent, full-duplex connection between browser and server
IndexedDB	A larger, transactional, asynchronous database in the browser (much bigger capacity than Web Storage)
Service Workers	A programmable network proxy running in the background — the basis of offline support and installable PWAs
Web Audio	Low-level, precise audio synthesis and processing in the browser
Battery Status	Read the device battery level and charging state (largely removed from most browsers today over fingerprinting concerns)

A Rough Mental Model

Storage & data: Web Storage, IndexedDB, Cache API, File API.
Device & environment: Geolocation, Battery Status (mostly retired), Fullscreen, Clipboard.
Rendering & graphics: Canvas, WebGL, inline SVG, Web Animations API.
Networking: Fetch, WebSockets, Server-Sent Events, Service Workers.
UI & interaction: Drag and Drop, contenteditable, Notifications, Web Components.
Performance & background work: Web Workers, Service Workers, requestIdleCallback.

Feature Detection Before Feature Use

Browser support varies across these APIs, especially the less common ones. Always check that an API exists before calling it, and provide a fallback or graceful no-op when it doesn't.

feature-detection.js

if ('geolocation' in navigator) {
  navigator.geolocation.getCurrentPosition(onSuccess, onError)
} else {
  console.log('Geolocation not supported — falling back to manual entry')
}

if ('clipboard' in navigator) {
  navigator.clipboard.writeText('Copied!')
}

if ('Notification' in window) {
  Notification.requestPermission()
}

MDN is the authoritative reference

This page is a map, not the full manual — for exact browser support tables, method signatures, and edge cases for any API listed here, MDN Web Docs is the best source of truth.

Why This Matters

Before this generation of APIs, doing any of the above in a browser usually meant reaching for a plugin (Flash, Silverlight, Java applets) or a server round-trip for things that are now instant and local. Together, these APIs are why "HTML5" became shorthand for "the web platform can now do almost anything a native app can."