useEffect-conditions.js

// GOOD! Place the condition inside the Hook
useEffect(() => {
  if (posts === null) {
    // This will run only if posts are not still fetched.
    // If you mount this component more than once,
    // the request won't beexecuted again
    getPosts();
  }
}, []); // Besides, with the empty array this Effect just run once


// BAD! Wrapping the Effect insithe the condition
if (posts === null) {
  useEffect(() => {
    getPosts();
  }, []);
}