How to use the destroyed function in Vue documentation

Vue.js is a popular JavaScript framework designed to provide developers with powerful tools and technologies to build large, complex web applications. The Vue.js framework provides some very useful life cycle hook functions, including the destroyed function. This article will introduce in detail how to use the destroyed function in the Vue document.

What is the destroyed function?

In the Vue.js framework, each component has a life cycle. During the component's life cycle, the Vue.js framework will call some specific functions at different points in time. These hook functions provide developers with ways to handle specific lifecycle events. Among them, the destroyed function is a function called after the Vue component is destroyed, completely unloaded from the DOM, and all event listeners and sub-component instances are also removed.

When we need to clean up the variables held by the component, release resources, or stop the timer after the Vue component is destroyed, we can use the destroyed function to perform these operations. In the destroyed function, we can access all properties, methods and states of the component instance, and can also modify, release or reset it.

The syntax of the destroyed function

The following is the basic syntax of the destroyed function:

new Vue({
  destroyed: function () {
    // 在这里执行一些清理操作和资源释放操作
  }
})

Parameters of the destroyed function

Because the destroyed function is only used after the component is destroyed will be called, so it doesn't require any parameters. However, within this function, we have access to all properties, methods, and state of the component instance, and can also modify, release, or reset it.

The return value of the destroyed function

Since the destroyed function is usually used to perform some cleanup operations and resource release operations, it usually does not return any value. However, if you need to return a value in the destroyed function, the Vue.js framework will ignore this value.

Application scenarios of the destroyed function

The destroyed function is usually used to perform some cleaning operations and resource release operations, such as:

Release the memory occupied by the component

When a Vue component is destroyed, the memory it occupied should be released to avoid memory leaks. In the destroyed function, we can manually delete variables held by the component, release resources, or cancel unfinished asynchronous operations to ensure that the memory occupied by the component is completely released.

new Vue({
  data: function () {
    return {
      largeArray: new Array(1000000)
    }
  },
  created: function () {
    console.log('Component created');
  },
  destroyed: function () {
    console.log('Component destroyed');
    this.largeArray = null; // 释放组件占用的内存
  }
})

Stop timer

In Vue components, timers are usually needed to perform some periodic operations, such as polling the backend API, refreshing the UI and other tasks. When a Vue component is destroyed, if the timer is not stopped, it may cause performance issues or other abnormalities. In the destroyed function, we can stop all outstanding timers to ensure that the component will not continue to occupy CPU resources after being destroyed.

new Vue({
  data: function () {
    return {
      timerId: null
    }
  },
  created: function () {
    this.timerId = setInterval(function () {
      console.log('interval running');
    }, 1000);
  },
  destroyed: function () {
    clearInterval(this.timerId); // 停止定时器
  }
})

Unsubscribe

In Vue components, you usually need to subscribe to some events or messages to perform some operations, such as monitoring user operations, processing back-end updates and other tasks. When a Vue component is destroyed, if the subscription is not canceled, it may cause a memory leak or other abnormal conditions. In the destroyed function, we can cancel all outstanding subscriptions to ensure that the component does not continue to receive messages after being destroyed.

new Vue({
  created: function () {
    this.$bus.$on('some-event', function () {
      console.log('event received');
    });
  },
  destroyed: function () {
    this.$bus.$off('some-event'); // 取消订阅
  }
})

Summary

The destroyed function is one of the life cycle hooks provided by the Vue.js framework, which is used to perform some cleanup operations and resource release operations after the Vue component is destroyed. Using destroyed functions avoids memory leaks and other performance issues, and keeps your code clean and maintainable when components are destroyed. In actual development, we should make full use of the destroyed function to clean up variables held by components, release resources, or stop timers and other operations, thereby improving the reliability and performance of the application.

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