The solution is to let know useEffect() that the closure log() depends on count and properly handle the reset of interval: With the dependencies properly set, useEffect() updates the closure as soon as count changes.
No spam, ever. Open the demo. App state consistently stays in inactive state while the notification window is dragged down.
npm: 3.10.8 If you find yourself adding a lot of event listeners using useEffect you might consider moving that logic to a custom hook.
Now drag down the notification window and monitor the console. you can click the array mutation version twice, and then the array
AppState.addEventListener('change', (state) => { console.log(state) }); Drag down the notification screen on iOS 11+ device. The 3 invocations of inc() increment value up to 3. you’d see that there is no number update happening. Has the issue been fixed, or does it still require the community's attention? The stale closure is solved. log() now logs the correct message "Current value is 3". https://reactjs.org/docs/hooks-reference.html#usestate.
the object instance is the same which will result in a stale value. Let’s find the closure that has captured the most up to date message variable. You signed in with another tab or window. Have a question about this project?
If you’re using React Hooks you might encounter a scenario where your
When even a bit of React can be a problem on devices slow and fast alike, using it is an intentional choice that effectively excludes people with low-end hardware. Later, even if count increases, log() still uses count as 0 from initial render. At first render, the closure log() captures count variable as 0. AppState.addEventListener('change' ... not giving proper results. In the recipe below we create a useEventListener hook that handles checking if addEventListener is supported, adding the event listener, and removal on cleanup. Xcode: Xcode 9.2 Build version 9C40b React onMouseEnter and onMouseOver examples The goal in this example is to make .innerBox appear and disappear when triggering one of these events.
If you’re using React hooks in a component with an event listener, your event listener callback cannot access the latest state. The counter displays the correct value 2. Since addToNumbers is mutating the state value directly it won’t
be properly updated. We can incorporate useRef to solve this problem. On first invocation of inc(), the closure log() has captured message variable having "Current value is 1". There’s another solution how to make log() work correctly. Hooks implementation assumes that between the component re-renderings, the latest closure supplied as a callback to the hook (e.g. The increment function increases an interval value by i, and returns a function that logs the current value: On the first call of inc(), the returned closure is assigned to the variable log. Open the fixed demo and click a few times increase.
actually rerender. the button is clicked 3 times it should show: 1,2,3. Inside the component
the hook useEffect() logs every second the value of count: Open the demo and click a few times increase button. Add this code to your app.js file. This is unexpected because value equals to 3. log() is a stale closure. ). Consider the following example which illustrates the issue. The component has 2 buttons: Now open the demo. The stale closure captures variables that have outdated values. By clicking “Sign up for GitHub”, you agree to our terms of service and 4. I have reviewed the documentation I have searched existing issues I am using the latest React Native version AppState.addEventListener('change', (state) => { console.log(state) }); Drag down the notification screen on iOS 11+ device. The key takeaway is to try to supply hooks with closures that have captured the freshest variables. Watchman: 4.9.0 I recommend to install eslint-plugin-react-hooks, which detects the forgotten dependencies. But closures are sometimes tricky. Important JavaScript concepts explained in simple words, Software design and good coding practices, 1 hour, one-to-one, video coaching sessions, JavaScript concepts teaching, workshops, or interview preparation (you choose!
Later on, if something else causes a rerender of the component you will Run your app.