StorageEvent

localStorage and sessionStorage localstorage

Baseline: Widely available on the web, in every major browser since Jul 2015, and long enough to count on (since Jan 2018).

niso: Partial 95%. 1239 of 1291 subtests pass, by system: Linux 95%, macOS 95%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · Storage, StorageEvent, Window

StorageEvent is an interface in idl/html.webidl, inheriting Event, exposed in Window. What it does is on MDN; this page says what niso has of it.

niso never fires storage events: each DOM has one document, so there is no other document to fire them at. Script can still make them.

Status

The web features its members belong to, each with its Baseline status on the web and how much of the feature’s WPT suite passes in niso (see Web platform support).

Feature	On the web	In niso	Members
localStorage and sessionStorage	Widely available	Partial 95% 1239 of 1291 subtests pass	7

Members

constructor

constructor

constructor(DOMString type, optional StorageEventInit eventInitDict = {});

int32_t niso_storage_event_new(niso_dom* dom, const char* type, size_t type_len, const niso_storage_event_init* event_init_dict, niso_handle* out);

key

attribute

readonly attribute DOMString? key;

int32_t niso_storage_event_get_key(niso_dom* dom, niso_handle self, niso_str* out);

oldValue

attribute

readonly attribute DOMString? oldValue;

int32_t niso_storage_event_get_old_value(niso_dom* dom, niso_handle self, niso_str* out);

newValue

attribute

readonly attribute DOMString? newValue;

int32_t niso_storage_event_get_new_value(niso_dom* dom, niso_handle self, niso_str* out);

url

attribute

readonly attribute USVString url;

int32_t niso_storage_event_get_url(niso_dom* dom, niso_handle self, niso_str* out);

storageArea

attribute

readonly attribute Storage? storageArea;

int32_t niso_storage_event_get_storage_area(niso_dom* dom, niso_handle self, niso_handle* out);

initStorageEvent()

operation

undefined initStorageEvent(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false, optional DOMString? key = null, optional DOMString? oldValue = null, optional DOMString? newValue = null, optional USVString url = "", optional Storage? storageArea = null);

int32_t niso_storage_event_init_storage_event(niso_dom* dom, niso_handle self, const char* type, size_t type_len, bool bubbles, bool cancelable, const char* key, size_t key_len, const char* old_value, size_t old_value_len, const char* new_value, size_t new_value_len, const char* url, size_t url_len, niso_handle storage_area);