I will use a debounce function as example.

const debounce = (func, wait) => {
  let timeout;

  return function executedFunction(...args) {
    const later = () => {
      clearTimeout(timeout);
      func(...args);
    };

    clearTimeout(timeout);
    timeout = setTimeout(later, wait);
  };
};

then I create a dummy function:

const dummy = () => console.log('debounced');

then I create a debouncedDummy function:

const debouncedDummy = debounce(dummy, 1000);

and then I call debouncedDummy multiple times:

debouncedDummy();
debouncedDummy();
debouncedDummy();
debouncedDummy();

What I need help understanding is why timeout variable is shared across multiple calls of debouncedDummy ?
What if timeout was defined outside the scope of debounce ?
What if timeout was defined inside the scope of executedFunction ?