How do you make sure that some operations are performed only once when using the useEffect hook in React's App.tsx?

In React applications, especially the App.tsx component, it is crucial to effectively manage the life cycle, especially when it comes to handling page refreshes and avoiding duplicate operations. This article will explore the behavior of the useEffect hook when the page is refreshed and provides a solution to ensure that certain operations are performed only once.

We analyze the following useEffect hooks:

 useEffect(() => {
  initAllState();
}, []);

Question 1: Will useEffect be re-executed after the page is refreshed? Is page refresh equivalent to project reloading?

The answer is yes. Page refresh clears the page content and re-executes all JavaScript code. The empty dependency array in the useEffect hook [] means that the effect is executed only once after the component is mounted. However, refreshing the page causes the component to be uninstalled and remounted, so initAllState function executes again. Page refresh is essentially reloading all resources, including HTML, CSS, and JavaScript, resulting in the loss of page status and all code rerunning.

Question 2: How to ensure that initAllState is executed only once and avoid duplicate network requests?

To avoid repeated execution of initAllState (especially in cases where network requests are included), you can add a flag inside the initAllState function to track whether it has been executed:

 function initAllState() {
  // Use localStorage or other persistent storage to save state if (localStorage.getItem('initAllState')) return;
  localStorage.setItem('initAllState', 'true');

  // Execute your initialization logic... For example:
  fetch('/api/data')
    .then(response => response.json())
    .then(data => {
      // Update application status})
    .catch(error => {
      // Handle error});
}

This method uses localStorage to store a flag bit. When initAllState is executed for the first time, the flag bit will be written localStorage ; when the flag bit is called again, it will be checked, and if it already exists, it will be returned directly to avoid repeated execution. This ensures that even if the page is refreshed, network requests in initAllState will only be executed once. Of course, other persistent storage mechanisms can also be used, such as sessionStorage (if the state only needs to be maintained in the current session) or more complex schemes. Which method to choose depends on your application requirements and persistence requirements for your state.

With the above improvements, even if the page is refreshed, network requests in initAllState will be executed only once, thereby improving application efficiency and avoiding unnecessary resource consumption. Remember to choose the persistent state storage method that suits your application scenario.

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