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; };}, []);
Question
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; };}, []);
Solution
The correct answer is A.
In option A, the useEffect hook is used to subscribe to the user when the component mounts. The variable isSubscribed is set to true, and then a GET request is made to an API. If the component is still mounted (i.e., isSubscribed is still true) when the response is received, the success handler is called.
The return function of the useEffect hook is a cleanup function that runs when the component unmounts. In option A, this function sets isSubscribed to false, effectively "unsubscribing" the user.
Option B is incorrect because the cleanup function sets isSubscribed to true, which would not unsubscribe the user.
Option C is incorrect because it does not include a cleanup function at all.
Option D is incorrect because it checks if isSubscribed is false before handling success, which is the opposite of what we want. Also, the cleanup function sets isSubscribed to true, which would not unsubscribe the user.
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
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
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))
What is the syntax for the useEffect() hook in React, when you want to run a function inside the useEffect only when the app loads?AuseEffect(() => {}, []);BuseEffect(() => {}, [stateVariable]);CuseEffect(() => {});DAll of the above
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.