Migrating to Vue 3 requires starting from four aspects: compatibility checking, responsive system changes, component communication adjustment, and building tool upgrade. First, check whether the project dependencies support Vue 3, especially core libraries such as Vuex and Vue Router, and consider using @vue/compat for gradual migration; second, the responsive system is implemented by Proxy, and ref/reactive needs to explicitly declare responsive data, replacing Vue.set; third, the life cycle hook is changed to onBeforeMount, onMounted, etc., and explicitly import and declare props/emits; fourth, if TypeScript is used, the configuration file and toolchain support need to be updated. It is recommended to complete the Vue 3 migration first and then gradually introduce TS, and pay attention to the adaptation method of Vite or Vue CLI to avoid excessive changes at one time to ensure a stable transition.

Migrating to Vue 3 is a step that many Vue 2 projects must face, especially since the official has stopped maintaining support for Vue 2. This process is not only about upgrading the version number, but also requires consideration of multiple aspects to ensure smooth migration and stable functions.

Compatibility and dependency checking

Before you start, you must first figure out whether your project is ready for migration. Vue 3 has some major changes in syntax and internal mechanisms, such as using Proxy to replace Object.defineProperty in Vue 2, which means that some old writing methods may no longer apply.

• Check whether the third-party library you use supports Vue 3, especially core dependencies such as Vuex, Vue Router, and Element UI.
• If you use the old way of registering components with Vue.extend or Vue.component, you must use the setup API or Composition API of Vue 3 instead.
• Using Vue 3 compatible builds (@vue/compat) can help you migrate step by step, but ultimately you will move to the standard Vue 3 writing.

It is recommended to use npm outdated or yarn outdated to see if there is an updated version of the dependency available, and then decide whether you need to upgrade the small version first.

Changes in data responsive systems

The underlying layer of Vue 3's responsive system uses Proxy and Reflect, which brings better performance and more flexible APIs, but also some differences in writing.

• If nested objects are no longer automatically converted to responsive, they need to be explicitly declared with reactive() or ref() .
• this is not available in the setup function, so if you rely heavily on this to access data, methods, etc. before, you need to adjust the logical structure.
• Methods like Vue.set or this.$set are abandoned in Vue 3, replaced by the correct way to directly assign values ??or use ref/reactive.

For example:
In the past, you might have written this way in Vue 2:

 this.someData = 'new value'

Now if it is in setup, you should use:

 const someData = ref('')
someData.value = 'new value'

Understanding these changes can help you avoid the problem of not updating data.

Component communication and life cycle hook adjustment

Vue 3's Composition API changes the way we organize component logic, and also affects how lifecycle hooks are written.

• The life cycle hook has changed from created , mounted , etc. onBeforeMount , onMounted , etc., and needs to be explicitly imported from vue .
• props and emits need to be explicitly declared in setup, otherwise it will not work properly.
• If you use provide/inject, you also need to pay attention to scope changes, especially how to use it under a combined API.

For example, call mounted in setup:

 import { onMounted } from 'vue'

onMounted(() => {
  // Initialization logic})

In addition, you should also pay attention to the naming specification when passing events. It is recommended to use kebab-case instead of camelCase to avoid compatibility issues.

Build Tools and TypeScript Support

Vue 3 supports TypeScript better, but it also means that if your project has not used TS, you may want to consider whether to introduce it during this migration.

• If you are using Vue CLI, just upgrade to the latest version and switch to the Vue version.
• If you are using Vite, it naturally supports Vue 3, making it easier to configure.
• If you plan to migrate to TypeScript at the same time, it is recommended to proceed in steps: first complete the migration of Vue 3, and then gradually add type definitions.

Some details:

• Modify the types in tsconfig.json to include vite/client (if it is Vite)
• Update the Babel plug-in and ESLint rules to be compatible with Vue 3 syntax
• Note whether <script setup></script> syntax sugar in the .vue file is in line with team habits

Basically, these are the main considerations. Although there will be many detailed problems during the migration process, most of them can be solved as long as they are done step by step. The key is to make assessments and plans in advance, and not make too many changes at once, as it is easy to make mistakes and is not easy to roll back.

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