Why does vue have a life cycle?

Vue.js is a popular front-end JavaScript framework that helps developers build dynamic web applications. A key feature of Vue.js is its lifecycle methods. Lifecycle methods are methods that run at specific points in time when called in a web application, and they allow developers to control the state and behavior of components.

Why does Vue.js have life cycle methods? What are they used for? In this article, we’ll discuss these issues and explore Vue.js lifecycle methods in action.

Lifecycle methods of Vue.js

In Vue.js components, lifecycle methods are a series of methods called in a specific order. These methods are called when the component is created, updated, or destroyed. Each method has its specific purpose and use case, and the order in which these methods are executed is called the "life cycle."

The life cycle methods of Vue.js are divided into three categories:

1. Creation cycle: a cycle that runs when the component is initialized, including beforeCreate, created, beforeMount and mounted.
2. Update cycle: a cycle that runs when data changes, including beforeUpdate and updated.
3. Destruction cycle: A cycle that runs when a component is destroyed, including beforeDestroy and destroyed.

These cycle methods allow developers to perform operations during the life cycle, such as initializing state, handling asynchronous data, registering event listeners, and cleaning up when the component is destroyed.

The Use of Lifecycle Methods

Building Vuejs components and adding event listeners, initial data, and component state can be difficult, especially for large applications. Vue.js provides some lifecycle methods that make it easier for developers to control the lifecycle of components. These methods allow developers to better manage components so that they execute at the right time.

The following is the purpose of each possible cycle:

• beforeCreate: Runs after the instance is created, but before data and events are set.
• created: A good time to determine if the data is ready and how it will be used before it is available.
• beforeMount: Runs before mounting DOM elements.
• mounted: The element is mounted, we can perform operations in this method
• beforeUpdate: When the component's data changes, this is a good time to do a final check before we modify the data. Any modifications that occur at this point in time will occur before the data is re-rendered.
• updated: Called when the data in the component has been changed and the DOM has been updated.
• beforeDestroy: Perform any cleanup operations before the component is destroyed, such as removing event listeners or canceling timers.
• destroyed: Components and instructions have been initialized and created, and memory and other resources are released at this stage.

For example, for Ajax calling process, we can use beforeCreate and created methods, because we need to get the data and ensure that the data exists in the instance scope. The beforeMount and mounted methods can be used to confirm whether a DOM element is available for update. If memory or other resources are used, you can use the beforeDestroy and destroyed methods to clean them up.

Practical application of life cycle methods

Consider the following example:

<script><br>export default {<br> data() {</p> <pre class="brush:php;toolbar:false">return {   message: &quot;Hello World&quot; };</pre> <p>},<br> created() {</p> <pre class="brush:php;toolbar:false">console.log(&quot;created called&quot;);</pre> <p>},<br> mounted() {</p> <pre class="brush:php;toolbar:false">console.log(&quot;mounted called&quot;);</pre> <p>},<br> updated() {</p> <pre class="brush:php;toolbar:false">console.log(&quot;updated called&quot;);</pre> <p>},<br> destroyed( ) {</p> <pre class="brush:php;toolbar:false">console.log(&quot;destroyed called&quot;);</pre> <p>}<br>};<br></script>

To facilitate demonstration and viewing of the execution of life cycle methods, the code outputs console.info(). In this example, we define the data attribute "message" and four lifecycle methods: created, mounted, updated, and destroyed.

During created, the console outputs "created called". This is because at this point Vue.js has internally completed the work of instantiating the component object and preparing data and events, but it has not yet been rendered to the page.

Next, we interact with the DOM in the mounted phase and output "mounted called". This is because it is visible during "mounted" and can interact with the DOM.

As the code continues to change, the data will also be modified. updated will be called whenever the data is updated. console.info() log output changes to "updated called".

Finally, when the component is destroyed, it calls destroyed. According to console.info(), "destroyed called" is output, stopping the use of resources in the instance and ending the component's life cycle.

Summary

Vue.js’s lifecycle methods are one of the core features of the framework because they allow developers to control the behavior and state of components. Lifecycle methods are executed in a specific order, allowing developers to do the right things at the right time, such as initializing the component, handling asynchronous data, registering event listeners, and cleaning up memory when the component is destroyed. The existence of life cycle methods allows developers to better manage the entire life cycle of the application, thereby providing an optimized application experience.

The above is the detailed content of Why does vue have a life cycle?. For more information, please follow other related articles on the PHP Chinese website!