Browser
Web APIs: the DOM, events, storage, and fetch.
- AbortControllerCancels an in-flight fetch (or other supporting async operation) via a shared signal, rejecting its promise with an AbortError.
- addEventListener and the Event ObjectRuns a function in response to a browser event, receiving an event object describing what happened and how to control the default behavior.
- consoleA host API for writing diagnostic output — not part of the JavaScript language itself, but available in both browsers and Node.
- CustomEventDispatches an application-defined event, carrying arbitrary data via .detail, decoupling the code that announces something from whatever reacts to it.
- fetchRequests a URL and returns a promise for the response — rejects only on network failure, not on an HTTP error status.
- Forms and Constraint ValidationHTML's built-in form validation attributes, and how to read validity state or add an accessible custom error message alongside it.
- IndexedDBA browser API for storing large amounts of structured, queryable data client-side, well suited to offline-capable applications.
- localStoragePersists small amounts of string data in the browser between page loads, scoped to the page's origin.
- Same-Origin Policy, CORS, and CSPThe browser's default restriction on reading cross-origin responses, how a server relaxes it with CORS, and how CSP restricts what a page can load.
- Selecting and Updating DOM ElementsquerySelector/querySelectorAll to find elements, and textContent/classList/setAttribute to read and update them safely.
- Service WorkersA script running independently of any page that intercepts network requests, enabling deliberate offline strategies.
- SharedArrayBuffer and AtomicsGenuine shared memory between workers, with Atomics providing race-free operations on it — requires cross-origin isolation headers.
- The History API (pushState and popstate)Changes the URL shown in the address bar without a page reload, and handles the browser's back/forward buttons — the mechanism client-side routers are built on.
- Trusted TypesA CSP-enforced browser API making a raw-string assignment to a DOM-XSS-sensitive sink a structural TypeError, unless it passes through a reviewed policy.
- Web WorkersRuns JavaScript on a separate thread for CPU-bound work, communicating with the main thread only via message passing.