simple observable pattern

observervable.ts

type Observer<T> = (value: T) => void;

export const observable = <T>() => {
  const observers: Observer<T>[] = [];
  return {
    subscribe: (observer: Observer<T>) => {
      observers.push(observer);
    },
    next: (value: T) => {
      observers.forEach(observer => {
        observer(value);
      });
    },
  };
};

const a = observable<number>();
a.subscribe(console.log);
a.next(42);
a.next(123);