Migrating from Vue 2 to Vue 3: A Complete Guide

With Vue 2 reaching its end-of-life on December 31, 2023, upgrading to Vue 3 is no longer a luxury, it is a necessity for security, performance, and future-proofing your applications. Vue 3 brings incredible improvements, including better TypeScript support, the Composition API, and a faster virtual DOM.

However, migrating a complex application is not simply updating a version number. It requires a strategic approach, this guide covers everything you need to know about Migrating from Vue 2 to Vue 3.

Why Migrate to Vue 3?

Vue 3 is a complete rewrite of the framework, optimized for modern web development. Key benefits include:

• Composition API: Allows better logic reuse and improved organization of large components.
• Better Performance: Up to 100% faster virtual DOM and improved rendering speed.
• Tree Shaking: Unused features are excluded from the final bundle, reducing file sizes.
• Teleport & Fragments: Simplifies handling modal components and allows multi-root components.

Pre-Migration Checklist

Before changing code, prepare your Vue 2 application:

1. Upgrade Vue 2: Ensure you are on the latest version of Vue 2 (2.7 or higher) as it backports some Vue 3 features.
2. Upgrade Ecosystem Tools: Upgrade Vue Router (to v4) and Vuex (or move to Pinia).
3. Use vue-compat (@vue/compat): This is a migration build that allows you to run Vue 3 while still using Vue 2 code, providing warnings for breaking changes.
4. Identify Dependencies: Check if your dependencies (libraries like Vuetify, Element UI) have Vue 3 compatible versions.

Key Breaking Changes (Vue 2 vs Vue 3)

The following changes are the most critical to address during migration:

1. Global API Changes (createApp)

Vue 2 used new Vue() to create an instance, which polluted the global state. Vue 3 introduces createApp.

Vue 2

import Vue from 'vue'  
import App from './App.vue'  
new Vue({ render: h \=\> h(App) }).$mount('\#app')

Vue 3

import { createApp } from 'vue'  
import App from './App.vue'  
createApp(App).mount('\#app')

2. V-Model Usage

In Vue 3, v-model props and events have been renamed.

• v-model -> modelValue
• v-model:name -> name
• @input -> @update:modelValue

3. V-For and V-If Precedence

In Vue 2, v-for had higher priority than v-if. In Vue 3, v-if has higher priority. You must restructure components that relied on the old behavior.

4. Fragment Components (Multi-Root Nodes)

Vue 3 supports multiple root nodes in a single file template, eliminating the need to wrap everything in a single <div>.

5. Filter Removal

Filters have been removed. Use computed properties or method calls instead.

Migration Strategies: Gradual vs. Big Bang

• Gradual Migration (@vue/compat): Suitable for large apps. It allows you to run the app, see warnings, and fix them incrementally.
• Big Bang Migration: Best for small, simple projects where a rewrite is faster than debugging the migration build.

Step-by-Step Migration Process

1. Install the Migration Build: Replace vue with @vue/compat and add vue-template-compiler.
2. Configure Build Tools: Set up alias configuration to enable the compatibility mode in your webpack/vite config.
3. Fix Warnings: Run the application and address warnings provided by @vue/compat in the console.
4. Migrate Components: Convert mixins to composables and adopt the Composition API where beneficial.
5. Remove @vue/compat: Once all warnings are resolved, replace @vue/compat with the final vue package.

Need Expert Assistance?

Migrating from Vue 2 to Vue 3 can be complex, especially with large-scale enterprise applications. At CMARIX InfoTech, their team of expert developers specializes in Vue.js migration and upgrading services.

Whether you need to hire vue.js developers for a short-term project or require full-cycle development services, we ensure a seamless upgrade that boosts performance and scalability.

Conclusion

Migrating to Vue 3 is a strategic move that brings better developer experience and performance. By taking a structured approach, utilizing the vue-compat build, and addressing breaking changes methodically, you can modernize your applications successfully.