Persistent client-side storage, localStorage, sessionStorage, IndexedDB. Plain ESM module registered with createWorker({ mainThreadModules: { storage } }) (or the host field of packages.json); see host/README.md for the setup boilerplate.

from storage import local_set, local_get, idb_open, idb_put, idb_get
from "https://cdn.edgepython.com/std/json.wasm" import loads

local_set("theme", "dark")
print(local_get("theme")) # -> "dark"

db = idb_open("notes", 1, '{"stores":["items"]}')
idb_put(db, "items", "1", '{"title":"hello"}')
note = loads(idb_get(db, "items", "1"))

deno run -A npm:playwright install chromium # one-time
HOSTCAP=storage deno test --allow-all tests/ # from repo root

See tests/README.md for the corpus shape.

• KV handlers are sync. localStorage / sessionStorage are blocking by spec; handlers return strings or None. No await, no receive().
• IndexedDB handlers yield. They return a Promise on the JS side; the runtime parks the coro in WaitingHostCall until resolved, same shape as fetch() in network/.
• Values cross as JSON strings. Encode with json.dumps, decode with json.loads.
• Key listings are JSON arrays (keys can contain commas). Parse with json.loads.
• Handles are integer IDs for IndexedDB; local_* / session_* address global stores directly (no handle).

local_get, local_set, local_remove, local_clear, local_keys. Same surface for sessionStorage with the session_ prefix (session_get, …). Difference is lifetime: sessionStorage clears when the tab closes; localStorage persists.

local_set("theme", "dark")
print(local_get("missing")) # -> None
print(loads(local_keys())) # -> ["theme"]
local_remove("theme")
local_clear()

idb_open, idb_put, idb_get, idb_delete, idb_keys, idb_close.

# Schema declares the object stores to create on first open / version bump.
db = idb_open("notes", 1, '{"stores":["items","tags"]}')
idb_put(db, "items", "1", dumps({"title": "hello", "ts": 1234}))
item = loads(idb_get(db, "items", "1"))
keys = loads(idb_keys(db, "items"))
idb_close(db)

Because IndexedDB handlers yield, they compose with the scheduler:

items, tags = gather(idb_keys(db, "items"), idb_keys(db, "tags")) # parallel reads
item = with_timeout(0.5, idb_get(db, "items", "1")) # deadline

src/index.js is a factory () => handlers (same shape as dom, network). Two slices in src/main/ (kv, idb) close over a shared state (a handle table for open IDBDatabase instances) and merge with Object.assign. KV handlers call localStorage / sessionStorage directly; IDB handlers promisify native IDBRequests and the runtime parks until resolved.

MIT OR Apache-2.0