stores

The Svelte Store contract

A store must contain a .subscribe method, which must accept as its argument a subscription function(aka Subscriber or Callback). This subscription function must be immediately and synchronously called with the store’s current value upon calling subscribe. All of a store’s active subscription functions must later be synchronously called whenever the store’s value changes.
The .subscribe method must return an unsubscribe function(aka Unsubscriber). Calling an unsubscribe function must stop its subscription, and its corresponding subscription function must not be called again by the store.
A store may optionally contain a .set method, which must accept as its argument a new value for the store, and which synchronously calls all of the store’s active subscription functions. Such a store is called a writable store.

For interoperability with RxJS Observables, the .subscribe method is also allowed to return an object with an .unsubscribe method, rather than return the unsubscription function directly. Note however that unless .subscribe synchronously calls the subscription (which is not required by the Observable spec), Svelte will see the value of the store as undefined until it does.

Store Contract Documentation

Types Definition

T = TypeVar("T")
covT = TypeVar("covT", covariant=True)
Subscriber = Callable[[T], None] # a callback
Unsubscriber = Callable[[], None] # a callback to be used upon termination of the subscription
Updater = Callable[[T], T]
Notifier = Callable[[Subscriber], Union[Unsubscriber, None]]

class StoreProtocol(Protocol, Generic[covT]):
    ''' The Svelte Store ~~contract~~ protocol. '''
    def subscribe(self, subscriber: Subscriber[T]) -> Unsubscriber: ...

Readable: TypeAlias = StoreProtocol[T]

class Writable(Readable[T]):
    ''' Writable protocol'''
    def set(self, value: T) -> None: ...
    def update(self, updater: Updater[T]) -> None: ...

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Writable

 Writable (*args, **kwargs)

Writable protocol

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StoreProtocol

 StoreProtocol (*args, **kwargs)

The Svelte Store ~~contract~~ protocol.

Implementation

Writable Store

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Store

 Store (initial_value:Any=None, start:Notifier=<function noop>)

A Writable Store.

	Type	Default	Details
initial_value	Any	None	initial value of the store
start	Notifier	noop	A Notifier (Optional)
Returns	None

Writable Factory

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writable

 writable (value:~T=None, start:Callable[[Callable[[~T],NoneType]],Optiona
           l[Callable[[],NoneType]]]=<function noop>)

Creates a new Writable Store (A Writable factory).

	Type	Default	Details
value	T	None	initial value of the store
start	Notifier	noop	Optional Notifier, a function called when the first subscriber is added
Returns	Writable[T]		Writable Store

Readable Store

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ReadableStore

 ReadableStore (initial_value:T, start:Notifier)

A Readable Store.

	Type	Details
initial_value	T	initial value of the store
start	Notifier	function called when the first subscriber is added
Returns	None

Readable Factory

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readable

 readable (value:~T, start:Callable[[Callable[[~T],NoneType]],Optional[Cal
           lable[[],NoneType]]])

Creates a new Readable Store (A Readable factory).

	Type	Details
value	T	initial value of the store
start	Notifier	function called when the first subscriber is added
Returns	Readable[T]	Readable Store

Derived Store

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DerivedStore

 DerivedStore (s:Union[Store,list[Store]], *functions:Callable)

A Derived Store.

	Type	Details
s	Union[Store, listStore]	source store(s)
functions	Callable
Returns	None	a callback that takes the source store(s) values and returns the derived value

Derived Factory

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derived

Creates a new Derived Store (A Derived factory).

d = derived(a, lambda a: f"{a}")
d

r<0> $str: 'fonzie'

Pipe Operator

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show_doc

 show_doc (sym, renderer=None, name:Optional[str]=None, title_level:int=3)

Show signature and docstring for sym

	Type	Default	Details
sym			Symbol to document
renderer	NoneType	None	Optional renderer (defaults to markdown)
name	str \| None	None	Optionally override displayed name of `sym`
title_level	int	3	Heading level to use for symbol name