Introduction to component life cycle and application scenarios in Vue

Vue is a popular JavaScript framework known for its simplified development process and high scalability. One of the core concepts of Vue is componentization, which allows us to decompose the application into a series of independent and reusable components. Each component has a life cycle, which defines the stages in which the component is created, used, and destroyed. This life cycle can help us better understand how the component works and use different life cycle hooks in the application to complete specific tasks. In this article, we will introduce the component life cycle in Vue in detail and how to apply life cycle hook functions.

Component life cycle

In Vue, components have three cycle phases: initialization phase, running phase and destruction phase. Each stage has lifecycle hook functions for different tasks.

Initialization phase

In the initialization phase, the object instance of the component is created. At this stage, Vue performs some basic tasks, such as setting the component's properties and compiling the component's template. The initialization phase in the component life cycle includes the following four phases: creation, update, mount and destruction:

• beforeCreate phase: called after the instance is created, before data observation and event/watcher configuration .
• created stage: The instance has been completely created, data modification and instance methods can be called, and the DOM tree has not been mounted yet.
• beforeMount stage: It is called before the mounting starts. At this time, the template is compiled into the render function. The render function is called for the first time. The mounting method before virtual DOM rendering is triggered. You can use this hook function. to change the rendered content.
• mounted stage: Executing to this step indicates that the component has rendered the virtual DOM into a real DOM node. At this time, you can access the DOM node of the component. If you use watch/listen, you can initialize it in the mounted stage.

Running phase

After the component is rendered, enter the running phase. At this stage, we can access the rendered DOM nodes and execute the component's methods. The running phase in the component life cycle includes the following phases:

• beforeUpdate phase: called before data update, that is, the hook function triggered before data update data is re-rendered
• updated phase : Called after re-rendering the component and updating the changes to the DOM node. DOM operations can be performed at this time.

Destruction Phase

Before the component is destroyed, we usually need to perform some cleanup operations, such as removing event listeners and cleaning up other resources. There is only one destruction phase in the component life cycle:

• beforeDestroy phase: called before the component is destroyed, when the instance can still be used.
• destroyed phase: Called after the component is destroyed. At this point the component instance has been cleaned up.

Application scenarios of each life cycle

Each life cycle hook function has different application scenarios. In the following sections, we will introduce some common application scenarios.

beforeCreate

In this hook function, the component's data and instances have not yet been initialized. A common use of this hook function is to perform some asynchronous operations before instantiation, such as reading configuration files and dynamically getting the properties of the component. In this hook function, we cannot access the component's data and methods, but we can access the Vue instance and the native DOM API.

created

In this hook function, the component's data and instance have been initialized. At this point, we have access to the component's properties and methods. A common use for this hook function is to perform some asynchronous operation after initialization, such as sending an HTTP request or getting data from the server. It's also common to set the component's default values ​​in this hook function when creating the component.

beforeMount

In this hook function, the template has been compiled but has not yet been rendered into the DOM. At this point, we can get the virtual DOM of the component and change the rendering result of the component by modifying it. A common use of this hook function is to perform DOM operations before the component is mounted to the DOM tree, such as printing some debugging information before the component is rendered, or adding some dynamic CSS classes.

mounted

In this hook function, the component has been mounted into the DOM tree. At this point, we can access the component's DOM node and control the rendering results by manipulating it. A common use for this hook function is to perform some action after the component is rendered, such as initializing a plugin, binding an event listener, or sending statistics.

beforeUpdate

In this hook function, the component's data has been updated, but the rendering result has not yet been updated. At this point, we can obtain the data and DOM nodes before the update, and modify the rendering results based on them. A common use for this hook function is to perform some operation before the component is updated, such as copying data, saving state, or recording changes.

updated

In this hook function, the rendering result of the component has been updated. At this point, we can access the updated DOM node and perform subsequent operations. A common use for this hook function is to perform some action after the component renders, such as updating plugins, analyzing performance, or sending statistics.

beforeDestroy

In this hook function, the component is about to be destroyed, but its DOM nodes and status are still accessible. A common use of this hook function is to clean up some resources before the component is destroyed, such as removing event listeners or canceling asynchronous operations.

destroyed

In this hook function, the component has been destroyed, and its DOM nodes and state are no longer available. A common use of this hook function is to perform some final operations after the component is destroyed, such as recording user logs or clearing the cache.

Summary

Vue’s component life cycle provides a wealth of hook functions that can help us complete a variety of tasks. Each lifecycle stage and hook function has different purposes and application scenarios. In practice, it is very important to understand the life cycle of components, because this can help us better understand how Vue works and make reasonable design and development in the application.

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