minimal implementation of signal

signal.js

const signal = (value) => {
    const fn = () => value;
    let subscribers = [];

    const notifySubscribers = () => {
        subscribers.forEach((subscriber) => subscriber(value));
    };

    fn.set = (newValue) => {
        value = newValue;

        notifySubscribers();
    };

    fn.update = (callback) => {
        value = callback(value);

        return value;
    };

    fn.subscribe = (callback) => {
        const count = subscribers.push(callback);

        return {
            unsubscribe: () => {
                subscribers = subscribers.slice(0, count - 1);
            },
        };
    };

    return fn;
};