Options API vs Composition API decision in Vue - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the main difference between Options API and Composition API

Which statement best describes the key difference between Vue's Options API and Composition API?

A Options API is only for Vue 2, and Composition API is only for Vue 3, so they cannot be used together.

B Options API organizes code by options like data, methods, and computed, while Composition API organizes code by logical features using functions.

C Options API requires class components, while Composition API only supports functional components.

D Options API uses reactive refs by default, while Composition API does not support reactivity.

💡 Hint

Think about how code is grouped and reused in each API style.

The Options API groups code by options like data, methods, and computed. The Composition API groups code by logical concerns using functions and reactive references, making it easier to reuse and organize complex logic.

❓ component_behavior

intermediate

Behavior difference in reactive state declaration

Consider these two Vue components. What is the main difference in how their reactive state is declared and accessed?

Component A (Options API):
export default {
  data() {
    return { count: 0 };
  },
  methods: {
    increment() {
      this.count++;
    }
  }
}

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

A Component A uses a plain property accessed with 'this.count', Component B uses a ref accessed with 'count.value'.

B Component A uses refs accessed with 'count.value', Component B uses plain properties accessed with 'this.count'.

C Both components use refs but Component A returns them from data(), Component B returns them from setup().

D Component A cannot update count reactively, Component B updates count reactively.

💡 Hint

Think about how reactive variables are accessed differently in Options API vs Composition API.

In Options API, reactive state is declared as plain properties inside the data() function and accessed with this.count. In Composition API, reactive state uses ref and must be accessed with count.value.

📝 Syntax

advanced

Identify the correct Composition API setup function syntax

Which option shows the correct syntax for a Vue 3 Composition API setup function that returns a reactive variable and a method?

A

setup() {
  const message = ref('Hello');
  function update() {
    message.value = 'Hi';
  }
  return { message, update };
}

B

setup() {
  let message = 'Hello';
  function update() {
    message = 'Hi';
  }
  return { message, update };
}

C

setup() {
  const message = reactive('Hello');
  function update() {
    message = 'Hi';
  }
  return { message, update };
}

D

setup() {
  const message = ref('Hello');
  function update() {
    message = 'Hi';
  }
  return { message, update };
}

💡 Hint

Remember how to update a ref's value inside a function.

Option A correctly declares a ref and updates its value using message.value. Option A uses a plain variable which is not reactive. Option A incorrectly uses reactive on a string (should be an object). Option A tries to assign directly to the ref variable instead of its .value.

🔧 Debug

advanced

Debugging reactivity loss in Options API vs Composition API

Why does this Composition API code fail to update the displayed count, while the Options API version works?

Composition API snippet:
setup() {
  let count = 0;
  function increment() {
    count++;
  }
  return { count, increment };
}

A Because <code>count</code> should be declared inside <code>data()</code> instead of <code>setup()</code>.

B Because <code>increment</code> is not declared as an arrow function, so it loses context.

C Because <code>count</code> is a plain variable, not a ref, so Vue cannot track changes to it.

D Because the <code>return</code> statement is missing parentheses around the object.

💡 Hint

Think about what makes a variable reactive in Composition API.

In Composition API, variables must be wrapped in ref() or reactive() to be reactive. Declaring count as a plain number means Vue cannot detect changes, so the UI does not update.

❓ state_output

expert

Predict the rendered output after state changes in mixed API usage

Given this Vue 3 component mixing Options API and Composition API, what will be the final rendered count after calling incrementBoth() once?

export default {
  data() {
    return { countOptions: 0 };
  },
  setup() {
    const countComposition = ref(0);
    function incrementBoth() {
      this.countOptions++;
      countComposition.value++;
    }
    return { countComposition, incrementBoth };
  }
}

Template displays: {{ countOptions }} - {{ countComposition }}

A 0 - 0

B 1 - 1

C 1 - 0

D 0 - 1

💡 Hint

Consider the context of this inside incrementBoth in Composition API.

Inside the setup() function, this is undefined. So this.countOptions++ does not update the Options API state. Only countComposition.value++ updates, so the rendered output is 0 - 1.

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