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Creating
Reading
Writing
Dependencies
Deriving
Create reactive values, read and write them, track their dependents, and derive new signals.
Creating
signal
signal(initialValue, options);Creates a reactive value.
Parameters
| Name | Type | Description |
|---|---|---|
| initialValue | any | The starting value |
| options | object | Optional configuration |
Options
| Name | Type | Default | Description |
|---|---|---|---|
| safety | 'clone' | 'reference' | 'none' | 'reference' | Value-protection preset. See Signal Options |
| equality | function | deep equality | Decides whether a new value differs from the current one. Snapshotted at construction |
| clone | function | structured clone | Copies values under safety: 'clone' and for change detection in mutate |
| id | function | id ?? _id ?? hash ?? key | Resolves an array item’s identity for the collection helpers |
| version | number | 0 | Seeds the change counter, for aligning with an external store’s revision |
Example
Reading
get
signal.get();Returns the current value and subscribes the running reaction.
Returns
The current value.
value
signal.value;signal.value = newValue;Property accessor for the signal. Reading subscribes the running reaction like get(), assigning sets the value like set().
Returns
The current value.
peek
signal.peek();Returns the current value without subscribing. Under safety: 'clone' the result is still a defensive copy.
Returns
The current value, with no dependency registered.
Example
raw
signal.raw();Returns the underlying stored value with no dependency tracking and no clone protection, even under safety: 'clone'.
raw() returns the actual stored object, not a copy. Mutating it bypasses change detection. Prefer peek() unless you specifically need the stored reference.
raw() returns the actual stored object, not a copy. Mutating it bypasses change detection. Prefer peek() unless you specifically need the stored reference.
Returns
The live stored value.
Writing
set
signal.set(newValue);Sets a new value, notifying dependents when it differs by the equality check.
Parameters
| Name | Type | Description |
|---|---|---|
| newValue | any | The value to store |
mutate
signal.mutate(mutationFn);Updates the value through a callback. Return a new value to set it, or mutate the current value in place and reactivity fires only if it changed.
Small values are passed to the callback directly. Large values are passed as a write-tracking wrapper (it shows as Proxy(Object) in the console) so detection costs the writes you make, not the size of the value. The wrapper is only valid inside the callback, and changes are detected through it — writes made through outside references won’t fire at that scale.
Parameters
| Name | Type | Description |
|---|---|---|
| mutationFn | function | Receives the current value, optionally returns a new one |
Usage
const items = signal(['apple', 'banana']);
// return a new valueitems.mutate(list => [...list, 'cherry']);
// or mutate in placeitems.mutate(list => { list.push('date'); });Example
clear
signal.clear();Sets the value to undefined, notifying dependents if it was not already undefined.
Example
Dependencies
depend
signal.depend();Subscribes the running reaction without using the value, the same as writing const ignore = signal.get(). Use it when a reaction should re-run on a change but reads the value from elsewhere.
Example
notify
signal.notify();Force-triggers dependents without changing the value, bypassing the equality check. Pair it with an in-place mutation under safety: 'reference' when the reference has not changed but dependents need to know.
Example
hasDependents
signal.hasDependents();Reports whether any reaction is currently subscribed to this signal.
Returns
true if at least one reaction depends on the signal.
Example
version
signal.version;signal.version = revision;A monotonic integer that increments inside notify(), so it advances on every announced change: a set() to a non-equal value, an in-place mutation helper, or a force notify(). A set() that the equality check treats as a no-op leaves it unchanged. Reading it does not subscribe the running reaction.
Assign to it to realign with an external store’s revision. Seed the starting value with the version option on signal().
Returns
The current change count, starting at 0.
Example
Deriving
derive
signal.derive(computeFn, options);Creates a new signal computed from this one, recomputing when this signal changes. Sugar for the free derive. For combining several sources see computed.
Parameters
| Name | Type | Description |
|---|---|---|
| computeFn | function | Receives this signal’s value, returns the derived value |
| options | object | Optional configuration, same shape as signal() |
Returns
A new Signal holding the derived value.