Migrating Large Applications to Vue.js 3

Anton Ioffe - December 24th 2023 - 9 minutes read

In the rapidly evolving landscape of web development, staying up-to-date with the latest frameworks is pivotal for performance-driven and scalable applications. Vue.js 3 emerges as a beacon of innovation, offering a suite of enhanced features and optimizations that promise to bring excellence to your large-scale projects. In this article, senior developers will be guided through the meticulous process of migrating substantial applications to Vue.js 3. From making a compelling case for migration to masterfully navigating its intricacies, and finally reaping the rewards of a transformed application, we'll embark on a comprehensive journey. You'll learn to craft a foolproof strategic migration plan, tackle the technical heavy-lifting with confidence, leverage cutting-edge features for architectural finesse, and manage post-migration with a sharp eye on performance and maintainability. Prepare to elevate your development prowess and push the frontiers of what's possible with modern JavaScript.

Assessing the Need for Migration to Vue.js 3

Considering the impending end of life (EOL) for Vue 2 at the end of 2023, the conversation about migrating to Vue.js 3 gains urgency. Beyond the baseline requirement of staying current with maintenance and support, the migration promises tangible, long-term benefits which need to be measured against the resource investment required to make the transition. With Vue.js 3 boasting up to 55% faster initial renders, 133% faster updates, and a 54% reduction in memory usage, the performance enhancements alone present a compelling case for migration. These figures not only highlight the framework's evolution but also suggest a direct impact on user experience and potentially a cost reduction in server resources due to the improved efficiency.

Vue.js 3's Composition API, designed to overcome limitations posed by the Options API in organizing and reusing code, is another considerable advantage. The Composition API offers a more flexible way to structure components by encapsulating logic into reusable functions. This leads to better scalability and maintainability, especially in large-scale applications. For developers, it translates to reassurance that the codebase can evolve without becoming overly complex or unwieldy as the application grows.

Enhanced TypeScript support is another significant enhancement, given the industry's growing preference for strongly-typed languages. Vue.js 3's adoption of TypeScript for its codebase has resulted in auto-generated type definitions which streamline developer experience with improved type inference and props type checking, even within templates. Employing TypeScript with Vue 3 not only promotes a more robust, error-resistant code base but also aligns with modern development practices that prioritize code safety and predictability.

However, it's essential to weigh these advantages against the challenges inherent to any significant version migration. Developers must navigate through breaking changes, dedicating time to learn new methodologies like the Composition API, and refactor existing code to align with Vue.js 3's reactivity model. Nonetheless, because Vue's core API remains consistent between versions, much of the Vue 2 knowledge base remains relevant, reducing the learning curve and facilitating a smoother transition than one might expect based on past experiences switching between major versions of other frameworks.

The performance improvements, better code organization, and stronger TypeScript integration constitute a substantial upgrade that goes beyond keeping the technology stack up to date. It's an investment in an application's future—its maintainability, scalability, and performance—which can significantly enhance the development process.

Crafting a Strategic Migration Plan

In the landscape of software development, crafting a strategic migration plan is analogous to charting a thoughtful course for a ship’s journey, one where navigational precision is essential. A meticulous assessment of the existing codebase lays the fundamental groundwork. This involves pinpointing Vue 2 specific constructs such as filters, event buses, or any direct DOM manipulations that are obsolete in Vue 3. Acknowledging deprecated patterns and assessing their prevalence across the codebase enables developers to gauge the migration's scope systematically.

Equally paramount is the preparation of a phased approach. The migration process benefits greatly from being segmented into planned releases — this is not a monolithic task but rather akin to strategic maneuvering through the stages of Install, Compatibility Check and Iterative Refactoring. Setting up separate development branches is crucial to strike a balance between stability and advancement. A vue2 branch can be maintained for existing workflow, while a vue3 branch is dedicated to migration efforts, ensuring that new features and fixes can continue to flow into the product without bottlenecking or conflation with migration tasks.

Crafting a comprehensive testing strategy ensures that regression is unlikely and that each release maintains functional integrity. This involves establishing robust unit and end-to-end tests, running full regression tests pre-transition, and adopting a continuous integration pipeline that can help to catch migration-related issues early on. Automated testing acts as a first defense, while manual testing by engineers well-versed in application intricacies serves to catch any nuanced deviations from expected behavior.

During the transition phase, it’s vital to implement mechanisms that ensure minimal disruption. This can be achieved through feature flagging, whereby new functionality powered by Vue 3 can be progressively released to subsets of users. Such toggle-based development allows for smoother phasing out of old features, safeguarding the user experience and solidifying confidence with every gradual release. It’s important for developers to harmonize the old with the new, integrating Vue 3 features in a manner that feels seamless to the end user.

Finally, underscoring the strategic plan is the acknowledgment that coordination and communication are bedrocks of a successful migration. The development team must keep an open channel for swift resolution of unforeseen complexities that invariably arise during substantial framework upgrades. Facilitating knowledge transfer sessions can enable team members to proficiently work with Vue 3's composition API and its reactivity system, circumventing common coding pitfalls and fostering a collaborative approach to problem-solving throughout the migration journey.

Overcoming Technical Hurdles in Migration

Migrating to Vue.js 3 introduces a profound change in reactivity handling compared to Vue 2’s Object.defineProperty methodology. With the new proxy-based reactivity system in Vue 3, the need for Vue.set and Vue.delete is eliminated, as reactivity for dynamic properties is inherently present. This simplification is evident in the revised way to update reactive state:

import { reactive } from 'vue';

const state = reactive({ myObject: {} });

function updateValue(key, value) {
    state.myObject[key] = value; // The proxy-based system tracks and reacts to changes automatically

Transitioning from the Options API to the Composition API necessitates rethinking and modularizing component organization. Despite Vue 2's Options API still being available, embracing the Composition API affords increased readability and maintainability. Converting computed properties from the Options API to the Composition API illustrates this modular approach:

import { ref, computed } from 'vue';

export default {
    setup() {
        const count = ref(0);
        const doubledCount = computed(() => count.value * 2);
        return { count, doubledCount };

To address breaking changes, a diligent review of migration warnings is imperative. Take the example of built-in filters, which are no longer supported in Vue 3. The following shows how to refactor a global filter into a composable function or method for use in templates:

function capitalize(value) {
    if (!value) return '';
    return value.charAt(0).toUpperCase() + value.slice(1);

// In a Vue 3 component
export default {
    methods: {

// Used in the template as {{ capitalize(value) }}

With Vue 3’s updates to lifecycle methods, developers must adapt their existing workflows, as with the transition from beforeDestroy to beforeUnmount, to accommodate the updated reactivity system:

// Vue 2
beforeDestroy() {
    // Perform necessary cleanup

// Vue 3
export default {
    beforeUnmount() {
        // Perform necessary cleanup, now aligned with Vue 3's reactivity system

Finally, the emits option significantly standardizes component-event interactions. Explicitly declaring event emissions in Vue 3, as opposed to the implicit approach in Vue 2, bolsters maintainability and facilitates debugging:

// Vue 2
this.$emit('custom-event', payload);

// Vue 3
export default {
    emits: ['custom-event'],
    setup(props, { emit }) {
        function doSomething(payload) {
            emit('custom-event', payload);

        return { doSomething };

Methodically addressing these key changes not only clarifies the aspects of Vue 3's API but also ensures a more efficient transition, enabling the development of resilient applications that exploit the capabilities of Vue.js 3.

Leveraging Vue 3's Advanced Features and Best Practices

Once the migration foundation is in place, developers can start to truly leverage the innovative features of Vue 3, which can dramatically enhance the architecture of large-scale applications. The introduction of fragments allows components to return multiple root nodes without the need for a wrapping element. This seemingly simple change reduces the need for additional <div> wrappers, resulting in cleaner DOM structures and improved rendering performance.

With teleport, developers can render content in different places in the DOM hierarchy, without changing the component hierarchy. This is particularly useful for modals, toasts, or tooltips that need to break out of their component confines to avoid styling or behavior issues due to the parent context. Best practices suggest that teleport should be used judiciously to maintain predictability in the document flow, and to always consider accessibility implications when moving focusable elements around the page.

Vue 3’s reactivity system has also undergone a major overhaul with the adoption of ES6 Proxies. This new system provides developers with fine-grained reactivity and makes writing reactive code simpler and more intuitive. It is also worth noting that when leveraging reactivity, it is best to initialize reactive state with a consistent structure and avoid dynamically adding or deleting reactive properties on the fly, which can lead to harder-to-track bugs.

In terms of modularity and reusability, the Composition API is central. It enables developers to encapsulate and reuse logic across components, leading to better organization and maintainability of complex codebases. To make the most out of this feature, one best practice is to write composable functions that are focused on a single aspect of functionality and then combine them in components as needed. This granularity not only improves reusability but also enhances testability, making it easier to write unit tests for isolated logic.

Lastly, application maintainability is significantly enhanced by adopting best practices such as using the <script setup> syntax sugar within Single File Components (SFCs) to reduce boilerplate, and employing state-driven CSS variables for reactive styles. This increases readability and maintainability, while making code changes more predictable and therefore less error-prone. Remember, each new feature should be integrated thoughtfully, prioritizing the overall coherence and stability of the application, and not just for the sake of novelty. How can these best practices be improved upon even further to harness the full potential of Vue 3 in your current project?

Analyzing Migration Impact and Post-Migration Care

Upon successful migration to Vue.js 3, a wave of immediate observations floods in; from tightened bundle sizes to a noticeable leap in runtime efficiency. A reduction in Javascript heap size, by as much as 20-30%, propels performance, particularly beneficial for applications dealing with complex data structures and lists. For CPU-intensive tasks, the newly optimized reactivity system of Vue 3 helps applications attain more responsive interfaces. Mirroring this is the subjective experience: applications feeling distinctly more agile and lighter in operation.

The journey, however, extends beyond the immediate aftermath and into the realm of post-migration care—a critical phase to ensure enduring benefits. Continuous performance monitoring is indispensable. Assessing application metrics post-deployment can spotlight any anomalies that slipped through testing, as well as confirm that the promised performance uplift is actualized. Tools that tracked performance in Vue 2 remain relevant but may now hone in on Vue 3’s nuances, such as its proxy-based reactivity.

Furthermore, debugging post-migration bespeaks its own set of challenges. Vue 3 introduces specific issues, notably around the Composition API’s reactivity nuances and the ref and reactive constructs. Developers acquainted with Vue 2's reactivity caveats must now pivot, translating their troubleshooting expertise to the new paradigms and patterns inherent in Vue 3. This includes a keen eye for memory leaks or unintended side effects caused by the reactive system's deep proxy-wrapping.

Acclimatizing the development team to the upgraded ecosystem is a subtle but significant part of post-migration care. It's one thing to translate an application to Vue 3, and quite another to enable a team to thrive in it. Ongoing learning initiatives, code reviews, and the cultivation of best practices help ensure that the team is not just surviving the migration but is proficient and productive, leveraging Vue 3's full spectrum of capabilities.

Lastly, painstaking attention is critical to the longevity of an upgraded codebase. Regular refactoring and codebase health checks are necessary to prevent regressions into outdated patterns and to maintain alignment with Vue 3's evolving best practices. Shared, modular components and utility functions within the code should be revisited for alignment with Vue 3’s Composition API, ensuring they are fashioned to facilitate both reusability and flexibility within the new Vue landscape.


The article "Migrating Large Applications to Vue.js 3" discusses the benefits and challenges of migrating substantial applications to Vue.js 3. It highlights the performance improvements, better code organization, and stronger TypeScript integration that Vue.js 3 offers. The article also provides a strategic migration plan, guidance on overcoming technical hurdles, tips on leveraging Vue 3's advanced features, and advice on post-migration care. A challenging technical task for readers could be to refactor a Vue 2 application to use Vue.js 3's Composition API, taking advantage of its modular approach to component organization and improved reactivity handling.

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