What happens if the cleanup function in the useEffect() hook returns a function?AThe returned function is ignoredBThe returned function is called before the effect runsCThe returned function is called after the effect runs and before the component unmountsDThe returned function is called after the component unmounts
Question
What happens if the cleanup function in the useEffect() hook returns a function?AThe returned function is ignoredBThe returned function is called before the effect runsCThe returned function is called after the effect runs and before the component unmountsDThe returned function is called after the component unmounts
Solution
The correct answer is C: The returned function is called after the effect runs and before the component unmounts.
Here's a step-by-step explanation:
-
The useEffect() hook is a function in React that allows you to perform side effects in function components. Side effects could be data fetching, subscriptions, or manually changing the DOM, etc.
-
The useEffect() hook takes two arguments: a function that contains the side-effect logic and an array of dependencies.
-
The function passed to useEffect() runs after the render is committed to the screen.
-
If this function returns a cleanup function, React will run that cleanup function before the component unmounts and also before subsequent runs of the effect due to updated dependencies.
-
Therefore, the cleanup function is used to clean up any resources that were allocated in the effect function. For example, if the effect function sets up a subscription, the cleanup function could cancel that subscription.
-
So, the returned function is not ignored, it's not called before the effect runs, and it's not called after the component unmounts. It's called after the effect runs and before the component unmounts, and also before subsequent runs of the effect due to updated dependencies.
Similar Questions
The useEffect cleanup is a function in the useEffect Hook that allows us to tidy up our code before our component unmounts. When our code runs and reruns for every render, useEffect also cleans up after itself using the cleanup function. Which of the foloowing is the correct Pseudo code for it?AuseEffect(() => { //effect //cleanup }, [input])BuseEffect(() => { // effect }, [cleanup])CuseEffect(() => { effect return () => { cleanup } }, [input])DNone of the above
What is the correct syntax of useEffect cleanup function?AuseEffect(() => { // effect return () => { // cleanup }}, [input])BuseEffect(() => { // effect // cleanup return () => { }}, [input])CuseEffect(() => { // effect return () => { }}, cleanup, [input])DNone of the above
Which of the following is the correct syntax for using the useEffect() hook with a cleanup function to start a timer?AuseEffect(() => { const timer = setInterval(() => { setCount(count + 1) }, 1000); return clearInterval(timer)}, [])BuseEffect(() => { const timer = setInterval(() => { setCount(count + 1) }, 1000); return () => clearInterval(timer)}, [])CuseEffect(() => { const timer = setInterval(() => { setCount(count + 1) }, 1000) }, [count]; return clearInterval(timer))DuseEffect(() => { const timer = setInterval(() => { setCount(count + 1) }, 1000) }, [count];return () => clearInterval(timer))
Which of the following code subscribes to the user in useEffect and then signout him in useEffect cleanup?AuseEffect(() => { // set our variable to true let isSubscribed = true; get(API).then((response) => { if (isSubscribed) { // handle success } }); return () => { // cancel the subscription isSubscribed = false; };}, []);BuseEffect(() => { // set our variable to true let isSubscribed = true; get(API).then((response) => { if (isSubscribed) { // handle success } }); return () => { // cancel the subscription isSubscribed = true; };}, []);CuseEffect(() => { // set our variable to true let isSubscribed = true; get(API).then((response) => { if (isSubscribed) { // handle success } });}, []);DuseEffect(() => { // set our variable to true let isSubscribed = true; if (!isSubscribed) { // handle success } return () => { // cancel the subscription isSubscribed = true; };}, []);
What does the useEffect hook do without a dependency array?
Upgrade your grade with Knowee
Get personalized homework help. Review tough concepts in more detail, or go deeper into your topic by exploring other relevant questions.