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# Vue3 app.onUnmount() Function Detailed Explanation * * Vue3 Global API](#) `app.onUnmount()` is an API used to add callback functions that execute when a component is unmounted. `app.onUnmount()` is a very useful API in Vue 3 that helps developers perform necessary cleanup operations when components are unmounted, avoiding memory leaks and resource waste. By using `app.onUnmount()` reasonably, you can improve the stability and performance of your application. * * * ## 1. What is `app.onUnmount()`? `app.onUnmount()` is a global API provided by Vue 3 that allows developers to add a callback function to the application instance, which is automatically executed when a component is unmounted. This feature is particularly suitable for cleaning up resources, canceling event listeners, or performing other operations that need to be handled when a component is unmounted. * * * ## 2. Basic Syntax ## Example app.onUnmount(()=>{ // Write code here that needs to be executed when the component is unmounted }); `app.onUnmount()` accepts a callback function as a parameter, which is automatically called when the component is unmounted. * * * ## 3. Use Cases ### 3.1 Cleaning Up Resources In components, we may create some resources that need to be cleaned up when the component is unmounted, such as timers, WebSocket connections, or third-party library instances. Using `app.onUnmount()` ensures that these resources are properly cleaned up when the component is unmounted. ## Example app.onUnmount(()=>{ clearInterval(timerID);// Clean up timer webSocket.close();// Close WebSocket connection }); ### 3.2 Canceling Event Listeners If global event listeners are registered in a component, to avoid memory leaks, these event listeners should be canceled when the component is unmounted. ## Example app.onUnmount(()=>{ window.removeEventListener('resize', handleResize);// Cancel window resize event listener }); ### 3.3 Canceling Subscriptions In components, we