Storage ​

The store/* namespace provides access to the browser's localStorage and sessionStorage APIs. Values are automatically JSON-serialized on write and JSON-parsed on read, so Sema types (strings, numbers, lists, maps) are preserved across storage round-trips.

localStorage ​

(store/get key) -> value | nil ​

Retrieve a value from localStorage. Returns nil if the key does not exist or if parsing fails.

sema
(store/get "username")        ;; => "alice"
(store/get "preferences")     ;; => {:theme "dark" :lang "en"}
(store/get "nonexistent")     ;; => nil

(store/set! key value) -> nil ​

Store a value in localStorage. The value is JSON-serialized.

sema
(store/set! "username" "alice")
(store/set! "count" 42)
(store/set! "todos" [{:text "Buy milk" :done false}])

(store/remove! key) -> nil ​

Remove a key from localStorage.

sema
(store/remove! "username")

(store/clear!) -> nil ​

Remove all keys from localStorage.

sema
(store/clear!)

(store/keys) -> list of strings ​

List all keys currently in localStorage.

sema
(store/keys)  ;; => ("username" "count" "todos")

(store/has? key) -> boolean ​

Check whether a key exists in localStorage.

sema
(if (store/has? "auth-token")
  (println "Logged in")
  (println "Not logged in"))

sessionStorage ​

Session storage functions mirror their localStorage counterparts but data is scoped to the browser tab and cleared when the tab closes.

(store/session-get key) -> value | nil ​

sema
(store/session-get "draft")

(store/session-set! key value) -> nil ​

sema
(store/session-set! "draft" "Work in progress...")

(store/session-remove! key) -> nil ​

sema
(store/session-remove! "draft")

(store/session-clear!) -> nil ​

sema
(store/session-clear!)

Type Preservation ​

Values are stored as JSON, so the following types round-trip correctly:

Sema TypeJSON Encoding
String"hello"
Number42, 3.14
Booleantrue, false
List[1, 2, 3]
Map{"key": "value"}
nilnull

Example: Persisting State ​

sema
;; Save state on change
(define (save-todos! todos)
  (store/set! "todos" todos))

;; Restore state on load
(define (load-todos)
  (or (store/get "todos") []))

;; Usage
(def todos (load-todos))
;; ... modify todos ...
(save-todos! todos)

Error Handling ​

Storage operations can fail (e.g., quota exceeded, storage disabled in private browsing). Every store/* function reports the error to the context's onerror handler and returns a fallback (nil, #f for store/has?, () for store/keys) rather than throwing.