Amend documentation for skipping useEffect

This is a documentation improvement request.

Currently https://reactjs.org/docs/hooks-effect.html#tip-optimizing-performance-by-skipping-effects explains skipping a useEffect based on a state variable by showing the following code:

useEffect(() => {
  document.title = `You clicked ${count} times`;
}, [count]); // Only re-run the effect if count changes

With the following explanation:

In the example above, we pass [count] as the second argument. What does this mean? If the count is 5, and then our component re-renders with count still equal to 5, React will compare [5] from the previous render and [5] from the next render. Because all items in the array are the same (5 === 5), React would skip the effect. That’s our optimization.

However, as the array we're shown only has a single element it, it is ambiguous what "all the items in the array" means. E.g. we cannot tell whether that's intentional phrasing, or just "plain English" that isn't actually tied to any technical precision.

Could this phrasing either be made more explicit, or (ideally) can an extra paragraph be added to explain what happens to an array with more than one element?

(originally filed as from https://github.com/facebook/react/issues/15068)

Bắt đầu với phần “Tip: Optimizing Performance by Skipping Effects” trong docs/hooks-effect.html, được liên kết trong issue. Xem lại phần giải thích về dependency array [count] và làm rõ cách các phép so sánh hoạt động khi một array có nhiều phần tử. Được xem là hoàn tất khi tài liệu giải thích rõ ràng, không mơ hồ về trường hợp có nhiều phần tử.