Confusing output in JavaScript when using setTimeout

Question

for (var i = 0; i < 3; i++) {
  const fun = () => console.log(i);
  
  setTimeout(() => {
    fun();
  }, 1000);
}

I got this output: 3 3 3. This will print 3 three times.

From MDN:

The global setTimeout() method sets a timer which executes a function or specified piece of code once the timer expires.