useState

useState<T>(initialValue: T): [T, (value: T) => void];

const body = () => {
    const [count, setCount] = useState(0)

    return VStack({ spacing: 12 }, [
        Text(String(count)).font("largeTitle"),
        Button("Increment", () => setCount(count + 1))
    ])
}

const body = () => {
    const [isVisible, setIsVisible] = useState(true)

    return VStack({ spacing: 16 }, [
        Button(isVisible ? "Hide" : "Show", () => {
            setIsVisible(!isVisible)
        }),
        isVisible ? Text("Now you see me").font("body") : Empty()
    ])
}

const body = () => {
    const [form, setForm] = useState({ name: "", email: "" })

    return VStack({ spacing: 12 }, [
        TextField("Name", form.name, (value) => {
            setForm({ ...form, name: value })
        }),
        TextField("Email", form.email, (value) => {
            setForm({ ...form, email: value })
        }),
        Text("Hello, " + form.name)
    ])
}