Vue 3 Composition API for Large Apps

Level: Intermediate to Experienced

As of October 3, 2025 — applicable for Vue 3.x (3.2+ recommended)

Prerequisites

This article assumes you have a working knowledge of Vue 3 fundamentals, including the Options API, reactive data, and component lifecycle hooks. Familiarity with ES modules, TypeScript (optional but helpful), and modern JavaScript syntax will be beneficial.

We’ll focus on Vue 3’s stable Composition API, introduced in Vue 3.0 and refined up to version 3.2+, which is the current mainstream standard for new large-scale Vue apps as of late 2025.

Have Node.js (v16+) and npm or yarn installed. Use vue@3.2+ or later for best TypeScript support and performance improvements.

Hands-on Steps for Scaling with the Composition API

1. Modularising Logic in Reusable Composables

One of the biggest advantages of the Composition API for large applications is the ability to extract reusable stateful logic into composable functions. These composables improve maintainability by separating concerns without relying on mixins or higher-order components.

Example: Here’s a simple composable managing form input state and validation.


// useFormInput.ts
import { ref, computed } from 'vue';

export function useFormInput(initialValue = '') {
  const value = ref(initialValue);
  const isValid = computed(() => value.value.trim().length > 0);
  function reset() {
    value.value = initialValue;
  }
  return { value, isValid, reset };
}

This function is separate from Vue components and can be imported wherever needed, encouraging code reuse.

2. Structuring Components for Clarity

In a large app, each component should be concise, ideally focusing on a single responsibility. Inside the setup() function, group related reactive state and methods to maintain readability.

Example of logical grouping with comments and clear returns:


import { defineComponent, reactive, watch } from 'vue';
import { useFormInput } from './useFormInput';

export default defineComponent({
  name: 'UserProfileForm',
  setup() {
    // State for inputs
    const nameInput = useFormInput('');
    const emailInput = useFormInput('');

    // Reactive form state
    const form = reactive({ touched: false });

    // Watch for email validity side-effect
    watch(() => emailInput.isValid, (valid) => {
      if (!valid) form.touched = true;
    });

    function submitForm() {
      if (nameInput.isValid && emailInput.isValid) {
        // submit logic
      }
    }

    return {
      nameInput,
      emailInput,
      form,
      submitForm,
    };
  },
});

3. TypeScript for Maintainability

Large Vue apps greatly benefit from TypeScript’s static typing. Vue 3’s Composition API works smoothly with TS, providing type inference within setup() and props.

Always type your composable functions and component props/emitters explicitly to avoid ambiguity in large codebases.

4. Shared State Management

For complex state across many components, consider the official Vue state library:

Pinia (recommended): The official state management library compatible with Vue 3 Composition API, simpler and more modular than Vuex.
Vuex 4: Still supported for Vue 3 but increasingly deprecated in favour of Pinia.

Use Pinia’s store syntax within Composition API easily:


import { defineStore } from 'pinia';

export const useUserStore = defineStore('user', {
  state: () => ({ user: null }),
  actions: {
    setUser(userData) {
      this.user = userData;
    },
    logout() {
      this.user = null;
    },
  },
});

Common Pitfalls to Avoid

1. Overusing Reactive APIs

Avoid wrapping every variable in ref() or reactive(). Use non-reactive variables for static data or computed properties where appropriate. Overusing reactivity can negatively impact performance and increase complexity.

2. Mixing Options API and Composition API Indiscriminately

While Vue 3 supports both APIs in the same project, avoid mixing them haphazardly within a single component. Prefer the Composition API exclusively in components for consistency, especially in large projects.

3. Not Leveraging TypeScript

Many large projects underestimate how much early TypeScript adoption reduces bugs and improves refactoring confidence. Start adding types early to reap maintainability benefits.

4. Neglecting Clear Return Values in `setup()`

Be explicit about what you return from setup(). Return only what the template or parent components need. This helps keep component API surface minimal and improves readability.

Validation Strategies

For large forms or dynamic fields, integrate validation libraries that are compatible with Composition API:

VeeValidate (3.x and 4.x) offers Composition API APIs for declarative validation.
Yup can be used for schema validation in conjunction with reactive state.

Example: Using VeeValidate’s useField and useForm functions.


import { defineComponent } from 'vue';
import { useForm, useField } from 'vee-validate';
import * as yup from 'yup';

export default defineComponent({
  setup() {
    const { handleSubmit } = useForm();
    const { value: email, errorMessage } = useField(
      'email',
      yup.string().email().required()
    );

    const onSubmit = handleSubmit(values => {
      // valid submission logic
    });

    return { email, errorMessage, onSubmit };
  },
});

Testing your composables and components with Vue Test Utils remains the standard approach. Mock reactive state or stores for unit tests and rely on integration tests for complex interaction.

Checklist / TL;DR

Use Vue 3.2+ to leverage Composition API optimisations and TypeScript integrations.
Extract reusable logic into composables to improve maintainability and testability.
Structure components with clear responsibilities and group related state/methods in setup().
Adopt TypeScript early for better developer experience and robustness.
Prefer Pinia for large-scale state management over Vuex.
Use validation libraries built for Composition API to simplify form validation.
Avoid mixing Options API and Composition API within a component; standardise on Composition API for consistency.
Keep returns from setup() minimal for clearer component APIs.

When to Choose Options API vs Composition API

Options API still offers a simple, intuitive syntax good for small apps, beginners, or quick prototyping. It groups code by options (data, computed, methods) but scales poorly in complex components.

Composition API is designed for large applications by grouping code by feature or logic type and improving TypeScript support. It’s the preferred API for medium to large apps due to improved reusability and organisation.