Detailed explanation of defineAsyncComponent function in Vue3: application of asynchronous loading components

Detailed explanation of defineAsyncComponent function in Vue3: Application of asynchronous loading components

In Vue3, we often encounter the need to load components asynchronously. At this time, we can use the defineAsyncComponent function provided by Vue3 to implement the function of loading components asynchronously. This article will introduce in detail the usage and application scenarios of the defineAsyncComponent function in Vue3.

1. Definition of defineAsyncComponent function

defineAsyncComponent is a function in Vue3, used to load components asynchronously. Its definition is as follows:

function defineAsyncComponent(loader) {
  if (__VUE_OPTIONS_API__) {
    return { __asyncLoader: loader, name: 'AsyncComponentWrapper' }
  }

  const AsyncComponent = defineComponent({
    name: 'AsyncComponentWrapper',
    setup() {
      const resolvedComponent = ref(null)
      const error = ref(null)
      const loading = ref(false)

      if (!loader) {
        error.value = new Error(`Error in async component: loader is undefined`)
      } else {
        loading.value = true
        loader().then((component) => {
          resolvedComponent.value = normalizeComponent(component)
        }).catch((err) => {
          error.value = err
        }).finally(() => {
          loading.value = false
        })
      }

      return { resolvedComponent, error, loading }
    },
    render() {
      const { resolvedComponent, error, loading } = this
      if (resolvedComponent) {
        return h(resolvedComponent)
      } else if (error) {
        throw error
      } else if (loading) {
        return h('div', 'Loading...')
      }
    }
  })

  AsyncComponent.__asyncLoader = loader

  return AsyncComponent
}

As can be seen from the code, the defineAsyncComponent function requires a loader function as a parameter, which should return a Promise and finally return a component in the resolve function.

2. Usage of defineAsyncComponent function

With the defineAsyncComponent function, we can use it to define a function that loads components asynchronously. For example:

import { defineAsyncComponent } from 'vue'

const AsyncComponent = defineAsyncComponent(() => {
  // 通过import函数异步加载组件
  return import('./components/AsyncComponent.vue')
})

export default {
  components: {
    AsyncComponent
  }
}

In the above code, we first use the defineAsyncComponent function to define a function AsyncComponent that asynchronously loads components, and use it as a subcomponent of our component and use it inside the component.

In addition to using the import function to load asynchronously, we can also use other asynchronous loading methods, such as:

const AsyncComponent = defineAsyncComponent(() => {
  // 使用动态import路径异步加载组件
  return import(`./components/${componentName}.vue`)
})

Through the above method, we can dynamically load different component paths and use defineAsyncComponent more flexibly. function.

When using asynchronous loading components, we need to pay attention to some details. Generally speaking, we need to define a caching strategy for asynchronously loaded components to avoid loading the same component repeatedly. We can use the keepAlive component provided by Vue to implement caching strategies. For example:

<template>
  <div>
    <keep-alive>
      <AsyncComponent :key="componentKey" />
    </keep-alive>
    <button @click="changeComponent">Change Component</button>
  </div>
</template>

<script>
import { defineAsyncComponent, ref } from 'vue'

export default {
  setup() {
    const componentKey = ref(0)

    const changeComponent = () => {
      // 每次更改组件的时候更新key，使组件重新渲染
      componentKey.value++
    }

    const AsyncComponent = defineAsyncComponent(() => {
      return import('./components/AsyncComponent.vue')
    })

    return { componentKey, changeComponent, AsyncComponent }
  }
}
</script>

In the above code, we define a counter componentKey to update the key value of the component, causing the asynchronously loaded component to be re-rendered. We also wrap the asynchronous loading component in a keep-alive component to implement the caching strategy.

3. Application scenarios of defineAsyncComponent function

The application scenarios of asynchronous loading components are very wide, especially in multi-page applications, it is often necessary to dynamically load different page components according to user needs. In addition, Vue3 also supports the use of defineAsyncComponent function to asynchronously load various other components such as instructions, plug-ins, templates, etc.

In Vue3, the defineAsyncComponent function has become one of the standard ways to implement asynchronous loading of components and is an important part of the Vue3 framework. By learning the usage and application scenarios of the defineAsyncComponent function, we can better grasp the essence of the Vue3 framework and flexibly apply it to project development.

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