Options API vs Composition API decision in Vue - Performance Comparison

Performance: Options API vs Composition API decision

MEDIUM IMPACT

This affects initial page load speed and runtime rendering performance by influencing bundle size and reactivity system efficiency.

Choosing between Options API and Composition API for a Vue 3 project

Vue

import { ref, onMounted } from 'vue';
export default {
  setup() {
    const count = ref(0);
    function increment() {
      count.value++;
    }
    onMounted(() => {
      console.log('Component mounted');
    });
    return { count, increment };
  }
}

Composition API groups reactive logic, enabling better tree shaking and smaller bundles, improving load speed and runtime efficiency.

📈 Performance Gainsaves ~5-10kb in bundle size; faster LCP and better runtime reactivity

Choosing between Options API and Composition API for a Vue 3 project

Vue

export default {
  data() {
    return { count: 0 };
  },
  methods: {
    increment() {
      this.count++;
    }
  },
  mounted() {
    console.log('Component mounted');
  }
}

Options API bundles all component options separately, which can increase bundle size and cause less efficient tree shaking.

📉 Performance Costadds ~5-10kb more to bundle compared to Composition API; slightly slower initial load

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Options API	Standard reactive bindings	Moderate reflows on state change	Moderate paint cost	[!] OK
Composition API	More granular reactive bindings	Fewer reflows due to optimized dependencies	Lower paint cost	[OK] Good

Rendering Pipeline

The Composition API reduces the amount of unused code included in the bundle and optimizes reactive updates, which streamlines the browser's style calculation and paint stages.

→JavaScript Parsing

→Style Calculation

→Layout

→Paint

⚠️ BottleneckJavaScript Parsing and Style Calculation due to reactive updates

Core Web Vital Affected

LCP

This affects initial page load speed and runtime rendering performance by influencing bundle size and reactivity system efficiency.

Optimization Tips

1Use Composition API to enable better tree shaking and smaller bundles.

2Composition API's granular reactivity reduces unnecessary DOM updates and reflows.

3Options API may increase bundle size and slow initial load compared to Composition API.

Performance Quiz - 3 Questions

Which API generally results in smaller JavaScript bundles in Vue 3?

A Both are equal

B Composition API

C Options API

D Neither affects bundle size

DevTools: Performance

How to check: Record a performance profile while interacting with the component; compare script evaluation and style recalculation times between Options and Composition API components.

What to look for: Look for shorter scripting and style recalculation times indicating better performance with Composition API.

Practice

1. Which Vue API organizes component code by options like data, methods, and computed?

easy

A. Options API

B. Composition API

C. Both APIs organize code this way

D. Neither API uses options

Solution

1. Step 1: Understand Options API structure

   The Options API groups code by options such as data, methods, and computed.

2. Step 2: Compare with Composition API

   The Composition API organizes code inside the setup() function by logical features, not by options.

3. Final Answer:

   Options API -> Option A

4. Quick Check:

   Options API groups by options like data and methods [OK]

Hint: Options API groups by options, Composition API uses setup() [OK]

Common Mistakes:

• Confusing Composition API with Options API structure
• Thinking both APIs organize code the same way
• Believing Options API uses setup() function

2. Which of the following is the correct way to declare a reactive state variable using the Composition API in Vue?

easy

A. const count = ref(0); inside setup()

B. data() { return { count: 0 } }

C. methods: { count() { return 0 } }

D. computed: { count: () => 0 }

Solution

1. Step 1: Identify Composition API reactive declaration

   In Composition API, reactive state uses ref() inside setup(), e.g., const count = ref(0);.

2. Step 2: Compare other options

   data() { return { count: 0 } } is Options API syntax, A and D are for methods and computed properties, not reactive refs.

3. Final Answer:

   const count = ref(0); inside setup() -> Option A

4. Quick Check:

   Use ref() in setup() for reactive state [OK]

Hint: Use ref() inside setup() for reactive state in Composition API [OK]

Common Mistakes:

• Using data() syntax in Composition API
• Confusing methods with reactive state
• Trying to declare reactive state outside setup()

3. Given this Vue component using Composition API:

import { ref } from 'vue';
export default {
  setup() {
    const count = ref(0);
    function increment() {
      count.value++;
    }
    return { count, increment };
  }
}

What will be the value of count after calling increment() twice?

medium

A. 0

B. 1

C. 2

D. undefined

Solution

1. Step 1: Understand ref and increment function

   count is a ref initialized to 0. Calling increment() increases count.value by 1 each time.

2. Step 2: Calculate count after two increments

   Starting at 0, after two increments: 0 + 1 + 1 = 2.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   Two increments add 2 to count.value [OK]

Hint: ref.value changes with increments; count.value++ twice = 2 [OK]

Common Mistakes:

• Forgetting to use .value with ref
• Assuming count is a plain number, not a ref
• Thinking increment does not change count

4. Identify the error in this Vue component using Options API:

export default {
  data() {
    count: 0
  },
  methods: {
    increment() {
      this.count++;
    }
  }
}

medium

A. Incorrect method name increment

B. data() should be a property, not a function

C. Using this.count instead of count

D. Missing return statement in data()

Solution

1. Step 1: Check data() function syntax

   In Options API, data() must return an object. Here, it lacks return keyword.

2. Step 2: Verify other parts

   Method name and usage of this.count are correct. data() is correctly a function.

3. Final Answer:

   Missing return statement in data() -> Option D

4. Quick Check:

   data() must return an object [OK]

Hint: data() must return an object with return keyword [OK]

Common Mistakes:

• Omitting return in data()
• Confusing this.count with count
• Thinking data() can be an object directly

5. You have a large Vue project with many components sharing logic like fetching data and handling loading states. Which API choice is best and why?

hard

A. Options API, because it separates code by options making it easier to read

B. Composition API, because it groups related logic together for better reuse

C. Options API, because it requires less code and is more modern

D. Composition API, because it avoids using setup() and is simpler

Solution

1. Step 1: Consider project size and logic reuse

   Large projects with shared logic benefit from grouping related code together for reuse and clarity.

2. Step 2: Compare API strengths

   Composition API allows grouping logic inside setup(), making reuse easier. Options API separates by options, which can scatter related logic.

3. Final Answer:

   Composition API, because it groups related logic together for better reuse -> Option B

4. Quick Check:

   Composition API groups logic for reuse in large projects [OK]

Hint: Use Composition API for reusable logic in big projects [OK]

Common Mistakes:

• Choosing Options API for better reuse in large projects
• Thinking Composition API avoids setup()
• Believing Options API is more modern