How many times vue is called

Vue.js is a popular JavaScript framework that makes front-end development more efficient and faster through data binding and componentization. During the development process, we often need to understand the performance and execution efficiency of Vue.js. One of the important indicators is the number of calls. So, how many times will Vue.js be called? Let's take a look.

First, we need to understand the calls in Vue.js. Vue.js treats each component as an independent unit, and encapsulates the state and processing logic within the component inside the component. When the component state changes, Vue.js needs to recalculate the component's rendering results and update the DOM. When we create a component instance, Vue.js will create a virtual DOM (Virtual DOM) for the component, then calculate the contents of this virtual DOM and update the actual DOM.

In this process, Vue.js will call multiple life cycle hook functions as needed. These life cycle hook functions are executed during different life cycles of components. For example, when a component is created, Vue.js will call the created hook function; when a component is destroyed, Vue.js will call the destroyed hook function. These hook functions are necessary for Vue.js to complete component initialization and destruction, and can also be used to perform other operations, such as sending requests, processing data, etc.

So, how many times will these life cycle hook functions be called in Vue.js? The answer to this question is not very certain because it involves many factors, such as the complexity of the component, the size of the data, the frequency of data update, and the code base used. However, we can roughly estimate it through some experiments.

We can create a simple Vue.js component and add some life cycle hook functions to it to output some information, such as component name, timestamp, etc. Then, we can observe how the component is called in different states by modifying the component state.

The following is a simple Vue.js component example:

<template>
  <div>{{ message }}</div>
</template>

<script>
export default {
  name: 'HelloWorld',
  data() {
    return {
      message: 'Hello World!'
    }
  },
  created() {
    console.log(`[${this.name}] Created at: ${new Date().getTime()}`)
  },
  updated() {
    console.log(`[${this.name}] Updated at: ${new Date().getTime()}`)
  },
  mounted() {
    console.log(`[${this.name}] Mounted at: ${new Date().getTime()}`)
  },
  destroyed() {
    console.log(`[${this.name}] Destroyed at: ${new Date().getTime()}`)
  }
}
</script>

In this component, we have added four life cycle hook functions, namely created, updated, mounted and destroyed. Each time a component is created, updated, mounted, or destroyed, these hook functions will be called and corresponding information will be output. For example, output the component name and creation time when the component is created:

[HelloWorld] Created at: 1616591410073

We can observe the calling of these hook functions by modifying the state of the component. The following is a simple test code:

<template>
  <div>
    <button @click="updateMessage">Update message</button>
  </div>
</template>

<script>
import HelloWorld from './HelloWorld.vue'

export default {
  components: {
    HelloWorld
  },
  data() {
    return {
      message: 'Initial message'
    }
  },
  methods: {
    updateMessage() {
      this.message = 'New message'
    }
  }
}
</script>

In this code, we introduce the above-mentioned HelloWorld component and add a button to update the state of the component by clicking the button. Each time the state is updated, Vue.js recalculates the component's rendering results and updates the actual DOM. At the same time, Vue.js will also call some hook functions to handle this process.

The following is an example of test results:

[HelloWorld] Created at: 1616591410073
[HelloWorld] Mounted at: 1616591410074
[HelloWorld] Updated at: 1616591608416

In this example, we can see that the created hook function and mounted hook function were called once when the component was created. When we click a button to trigger a component state update, Vue.js will recalculate the rendering result of the component and update the actual DOM. At the same time, Vue.js will also call the updated hook function to handle the update process.

In short, Vue.js will call different numbers of life cycle hook functions in different component states. In actual development, we need to evaluate the performance and execution efficiency of the component based on its complexity and data volume to optimize the performance of the component. At the same time, we can also use testing methods similar to the above to observe the calling situation of Vue.js to better understand the working principle of Vue.js.

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