VUE3 development basics: tutorial on using asynchronous components

Vue 3 is the latest major version of Vue.js, which has many new features and improvements compared to Vue 2. One of the most prominent improvements is the use of asynchronous components. In this article, we will delve into the usage and techniques of asynchronous components in Vue 3.

What is an asynchronous component?

In Vue, components can be introduced through the import statement or require function. These components are called synchronous components, and their code is loaded and compiled immediately when the application starts. However, as apps get larger, synchronously loaded components can cause longer first-screen load times and even consume large amounts of memory and bandwidth.

To solve this problem, Vue 3 provides the concept of asynchronous components. Asynchronous components are components that are loaded and compiled when needed. This means that when the application needs to load certain components, it will request these components asynchronously from the server and dynamically load and compile them after the response comes back. This can significantly reduce first-screen load times and reduce the application's memory footprint and bandwidth consumption.

How to use asynchronous components?

In Vue 3, asynchronous components can be defined in the following ways:

const AsyncComponent = defineAsyncComponent(async () => {
  // 异步加载和编译组件的代码
  const module = await import("@/components/AsyncComponent.vue")
  return module.default
})

The above code defines a component named AsyncComponent's asynchronous component. The way to define asynchronous components is similar to that of synchronous components, except that asynchronous components need to use the defineAsyncComponent function instead of the defineComponent function.

In the definition of an asynchronous component, we load and compile the code of the component asynchronously through the async and await keywords. In this example, we use the import statement to load the component from the @/components/AsyncComponent.vue file and return its default export. It should be noted that in the definition of an asynchronous component, we only need to return the default export of the component, not the Vue instance or component options.

Once we define the async component, we can use it in the parent component. For example, if we want to use the asynchronous component defined above in the App.vue component, we can do this:

<template>
  <div>
    <h1>异步组件</h1>
    <AsyncComponent />
  </div>
</template>

<script>
import { defineAsyncComponent } from "vue"
const AsyncComponent = defineAsyncComponent(async () => {
  const module = await import("@/components/AsyncComponent.vue")
  return module.default
})

export default {
  components: {
    AsyncComponent
  }
}
</script>

In the above code, in the components option The asynchronous component AsyncComponent is registered in. Then use the <AsyncComponent> tag in the template to display the asynchronous component.

When the parent component is rendered, Vue 3 will detect the <AsyncComponent> tag and then asynchronously request the asynchronous component we defined from the server. Once the asynchronous response comes back, Vue will dynamically load and compile the component and display it on the page.

In addition to the above method, we can also use other methods to define asynchronous components using the defineAsyncComponent function provided by Vue 3. For example, we can use a combination of dynamic import and the defineAsyncComponent function to define an asynchronous component:

const AsyncComponent = defineAsyncComponent(() => import("@/components/AsyncComponent.vue"))

We can also use traditional Promise syntax to define an asynchronous component:

const AsyncComponent = defineAsyncComponent(() =>
  new Promise(resolve => {
    setTimeout(() => {
      import("@/components/AsyncComponent.vue").then(module => {
        resolve(module.default)
      })
    }, 1000)
  })
)

In the above code, we use a Promise with a delay of 1 second to simulate asynchronous loading and compilation of components.

Conclusion

Asynchronous components are a powerful and useful feature in Vue 3. By using asynchronous components, we can significantly improve the performance and user experience of our applications. In this article, we take a deep dive into the usage and techniques of asynchronous components in Vue 3. I hope this article can help you understand and use Vue 3's asynchronous components.

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