useEffect Hook Rendering
We declare the count state variable, and then we tell React we need to use an effect. We pass a function to the useEffect Hook. This function we pass is our effect. Inside our effect, we set the document title using the document.title browser API. We can read the latest count inside the effect because it’s in the scope of our function. When React renders our component, it will remember the effect we used, and then run our effect after updating the DOM. This happens for every render, including the first one.
Experienced JavaScript developers might notice that the function passed to useEffect is going to be different on every render. This is intentional. In fact, this is what lets us read the count value from inside the effect without worrying about it getting stale. Every time we re-render, we schedule a different effect, replacing the previous one. In a way, this makes the effects behave more like a part of the render result — each effect “belongs” to a particular render.