5 min read1 hour ago

–

Learn how to refactor large Vue 3 codebases using the Factory Design Pattern. A practical guide for scalable frontend architecture using the Composition API.

In fast-evolving enterprise applications, frontend codebases often grow messy over time — tangled business logic, duplicated components, and composables that try to do everything at once. When that happens, scaling features becomes harder than adding new ones.

This article explores how applying the Factory Design Pattern in a Vue 3 Composition API setup can bring structure, scalability, and elegance back to your frontend architecture.

Why Refactoring Becomes Inevitable

Most frontend projects start small — a couple of forms, some API calls, and a few reusable components. But as features grow, we start adding more conditionals:

if (type === 'A') handleTypeA()else if (type === 'B') handleTypeB()else if (type === 'C') handleTypeC()

At first, this seems harmless. Over time, these conditionals start appearing everywhere — in composables, components, and even templates. The result?

• Hard-to-read code
• Duplicated logic
• Painful testing
• Increased onboarding time

When you start to see this pattern repeating across multiple modules, it’s time to consider design-level refactoring — not just “cleanup.”

Enter the Factory Design Pattern

In classic software architecture, the Factory Pattern abstracts the creation logic of objects, letting you instantiate the right implementation based on context — without the caller knowing how that decision is made.

In frontend architecture, this translates beautifully to composable design:

Let your composables return specialized feature logic dynamically, while sharing a common base for reusable functionality.

This pattern works especially well in Vue 3’s Composition API, because composables already behave like functions that return domain-specific state and behavior.

Press enter or click to view image in full size

Figure: High-level architecture showing how a Base Composable powers multiple specialized composables through a Factory function in a Vue 3 setup — ensuring scalable, modular frontend design.

The Problem: Duplicated Logic Across Similar Features

Imagine you’re building a system that manages multiple product types — say digital items, subscriptions, and physical goods. Each product type shares some core logic (fetching, updating, deleting) but also has unique rules (e.g., shipping validation, license generation).

Many teams end up doing this:

if (product.type === 'digital') {  // license logic} else if (product.type === 'physical') {  // shipping logic}

This works, until you have to touch it six months later.

The Scalable Solution: Factory-Driven Composables

Let’s approach it systematically.

We start by defining a base composable — the foundation that handles the common logic shared across all product types.

🔹 useProductBase.js

export function useProductBase() {  const loading = ref(false)  const product = reactive({})async function fetchProduct(id) {    loading.value = true    const response = await api.get(`/products/${id}`)    Object.assign(product, response.data)    loading.value = false  }  async function updateProduct(id, payload) {    loading.value = true    await api.put(`/products/${id}`, payload)    loading.value = false  }  return { product, loading, fetchProduct, updateProduct }}

This handles what every product needs — fetching, updating, and reactive state.

Now, we create specific composables that extend this base, adding unique domain logic.

🔹 useDigitalProduct.js

import { useProductBase } from './useProductBase'export function useDigitalProduct() {  const base = useProductBase()  async function generateLicense() {    console.log('Generating license for', base.product.name)  }  return {    ...base,    generateLicense  }}

🔹 usePhysicalProduct.js

import { useProductBase } from './useProductBase'export function usePhysicalProduct() {  const base = useProductBase()  async function validateShipping() {    console.log('Validating shipping address for', base.product.name)  }  return {    ...base,    validateShipping  }}

Building a Factory Function for Dynamic Composable Creation

Here’s where the Factory Pattern ties it all together — a single function that decides which composable to use based on context.

🔹 useProductFactory.js

import { useDigitalProduct } from './useDigitalProduct'import { usePhysicalProduct } from './usePhysicalProduct'import { useSubscriptionProduct } from './useSubscriptionProduct'export function useProduct(type) {  switch (type) {    case 'digital':      return useDigitalProduct()    case 'physical':      return usePhysicalProduct()    case 'subscription':      return useSubscriptionProduct()    default:      throw new Error(`Unknown product type: ${type}`)  }}

Now the component doesn’t need to care what kind of product it’s dealing with — it just calls useProduct(type) and gets the right behavior injected.

Why the Factory Pattern Fits Naturally into Vue 3’s Composition API

Vue 3’s Composition API embraces the principles of composition over inheritance, making it a perfect match for the Factory Pattern. By combining composables with factory-style logic, we achieve:

1. Decoupled feature logic Each composable focuses on one domain concern — perfect SRP (Single Responsibility Principle).
2. Predictable scalability When a new product type appears, you add a new composable — not a new “else if.”
3. Better testability Each composable can be unit tested in isolation.
4. Improved maintainability Shared logic lives in the base; specialized logic lives in extensions.

Real-World Architectural Impact

This design pattern scales beyond just composables — it’s a mindset. You can apply the same principle to:

• Form builders that generate inputs dynamically
• Report generation systems that vary by data type
• File handlers that differ by format
• Notification senders that route through email, SMS, or push APIs

By centralizing creation logic and distributing behavior, you’re effectively building a plugin-friendly architecture inside your app — one where new modules can be dropped in without breaking existing ones.

Vue 3 Best Practices for Factory-Driven Composables

Here are a few practical lessons from real-world implementations:

• Keep your base composable framework-agnostic (no template coupling).
• Always return pure state and actions — never expose internal refs directly.
• Document the expected API of each composable (inputs, outputs, async contracts).
• If possible, define TypeScript interfaces for stronger consistency across factories.
• Use lazy imports for factories if the number of specializations grows large.

The Takeaway

Refactoring using the Factory Design Pattern in Vue isn’t about introducing complexity — it’s about creating architectural simplicity that scales.

It lets your frontend evolve from a collection of components into a well-structured system of composable, reusable, and replaceable units.

When your app grows from dozens to hundreds of features, these patterns separate teams that maintain software from those that reinvent it.

✍️ Final Thoughts

As frontends become richer and enterprise-grade, adopting proven design principles like the Factory Pattern gives teams the architectural headroom to grow confidently. A small investment in structure today saves countless hours of debugging and refactoring tomorrow.

If your Vue composables are growing uncontrollably — consider a factory. You might just find elegance hiding behind that refactor.

If you found this useful, consider sharing it with your team or leaving a response. Let’s make frontend architectures as elegant as they are functional.