Vue gives you two ways to write component logic. Understanding both matters because you'll see Options API in legacy codebases and Composition API in everything new.

Options API

The Options API is the original Vue style. You export an object with predefined keys — data for state, methods for functions, computed for derived values, watch for side effects. Vue reads those keys and wires everything together behind the scenes.

<script>
export default {
  data() {
    return { count: 0 }
  },
  computed: {
    doubled() { return this.count * 2 }
  },
  methods: {
    increment() { this.count++ }
  }
}
</script>

This works fine for small components. The problem appears when a component grows: logic for a single feature (say, search) gets scattered across data, computed, methods, and watch. You end up jumping between sections to understand one feature.

Composition API

The Composition API (Vue 3) lets you write logic as plain JavaScript functions. Instead of splitting by option type, you group code by what it does.

<script setup lang="ts">
import { ref, computed } from 'vue'

const count = ref(0)
const doubled = computed(() => count.value * 2)
function increment() { count.value++ }
</script>

The reactive state (ref), derived values (computed), and functions all live together. When the component grows, you can extract related logic into a composable — a plain function that returns reactive state — and reuse it across components.

Why the Composition API wins for real projects

In a component with search, pagination, and filters using Options API, each feature's code is fragmented:

data()      → searchQuery, page, filters
computed    → filteredResults, totalPages, activeFilterCount
methods     → search(), nextPage(), toggleFilter()
watch       → searchQuery watcher, filters watcher

With the Composition API, each feature is a self-contained block (or composable) that you can read top-to-bottom without jumping around. That's the core difference: organization by feature instead of by option type.

Which should you learn?

Both. The Composition API with <script setup> is the recommended default for new projects. But you need to read Options API code because most existing Vue 2 apps use it, and many Vue 3 codebases mix both styles during migration.

See also: What is script setup? · What is a composable?

References

• Composition API FAQ - Vue.js docs
• Introduction: Options API vs Composition API - Vue.js docs
• script setup - Vue.js docs