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💎 The Signal Function: $( ) ​

The $( ) function is the core constructor of SigPro. It defines how data is stored, computed, and persisted.

🛠 Function Signature ​

typescript
$(initialValue: any, key?: string): Signal
$(computation: Function): ComputedSignal
ParameterTypeRequiredDescription
initialValueanyYes*The starting value of your signal.
computationFunctionYes*A function that returns a value based on other signals.
keystringNoA unique name to persist the signal in localStorage.

*Either an initial value or a computation function must be provided.

📖 Usage Patterns ​

1. Simple State ​

$(value) Creates a writable signal. It returns a function that acts as both getter and setter.

javascript
const count = $(0); 

count();    // Read (0)
count(10);  // Write (10)

2. Persistent State ​

$(value, key) Creates a writable signal that syncs with the browser's storage.

javascript
const theme = $("light", "app-theme"); 

theme("dark"); // Automatically calls localStorage.setItem("app-theme", '"dark"')

Note: On page load, SigPro will prioritize the value found in localStorage over the initialValue.

3. Computed State (Derived) ​

$(function) Creates a read-only signal that updates automatically when any signal used inside it changes.

javascript
const price = $(100);
const tax = $(0.21);

// This tracks both 'price' and 'tax' automatically
const total = $(() => price() * (1 + tax()));

🔄 Updating with Logic ​

When calling the setter, you can pass an updater function to access the current value safely.

javascript
const list = $(["A", "B"]);

// Adds "C" using the previous state
list(prev => [...prev, "C"]);
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