js signal simple implementation

signal_naive_impl.js

const signal = (value) => {
  const box = { value };
  const getter = () => {
    if (typeof box.value !== 'function') {
      return box.value;
    }
    return box.value();
  };
  getter.set = (newValue) => { box.value = newValue };
  getter.update = (callback) => { box.value = callback(box.value) };
  return getter;
};

const computed = (compute) => signal(compute);

// Usage examples for signal and computed

// Example 1: Basic signal usage
const count = signal(0);
console.log(count()); // Output: 0
count.set(5);
console.log(count()); // Output: 5
count.update(val => val + 1);
console.log(count()); // Output: 6

// Example 2: Signal with object
const user = signal({ name: 'John', age: 30 });
console.log(user().name); // Output: John
user.update(u => ({ ...u, age: u.age + 1 }));
console.log(user().age); // Output: 31

// Example 3: Computed signal
const celsius = signal(0);
const fahrenheit = computed(() => celsius() * 9/5 + 32);
console.log(fahrenheit()); // Output: 32
celsius.set(100);
console.log(fahrenheit()); // Output: 212

// Example 4: Nested computations
const a = signal(1);
const b = signal(2);
const sum = computed(() => a() + b());
const double = computed(() => sum() * 2);
console.log(double()); // Output: 6
a.set(3);
console.log(double()); // Output: 10

// Example 5: Signal with function value
const greet = signal(() => "Hello, World!");
console.log(greet()); // Output: Hello, World!
greet.set(() => "Bonjour, le monde!");
console.log(greet()); // Output: Bonjour, le monde!