Derived signals

Derived signals are functions that rely on one or more signals to produce a value.

These functions are not executed immediately, but instead are only called when the values they rely on are changed. When the underlying signal is changed, the function will be called again to produce a new value.

const double = () => count() * 2;

In the above example, the double function relies on the count signal to produce a value. When the count signal is changed, the double function will be called again to produce a new value.

Similarly you can create a derived signal that relies on a store value because stores use signals under the hood.

const fullName = () => store.firstName + ' ' + store.lastName;

These dependent functions gain reactivity from the signal they access, ensuring that changes in the underlying data propagate throughout your application. It is important to note that these functions do not store a value themselves; instead, they can update any effects or components that depend on them. If included within a component's body, these derived signals will trigger an update when necessary.

While you can create derived values in this manner, Solid created the createMemo primitive. Learn more about memos.