Why is useEffect running dispite of empty array of dependecies

Why is useEffect running after render?
There is no differnece between [] and [number] in this case.

import { useEffect, useState } from 'react';

export const Timer = () => {
  const [number, setNumber] = useState(0);


  useEffect(() => {
    let id = setInterval(() => setNumber((prev) => prev + 1), 1000);
    return () => clearInterval(id);
  }, []);

  return (
    <div>
      <h1>Timer</h1>
      <p>{number}</p>
    </div>
  );
};