Setup function basics in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a setup function that returns a reactive count variable.

Vue

<script setup>
import { ref } from 'vue'
const count = [1](0)
</script>

Drag options to blanks, or click blank then click option'

Acomputed

Breactive

Cref

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using reactive instead of ref for a primitive value.

Trying to use computed without a getter function.

The ref function creates a reactive reference to a value, which is perfect for simple reactive variables like count.

2fill in blank

medium

Complete the code to define a setup function that returns a method to increment count.

Vue

<script setup>
import { ref } from 'vue'
const count = ref(0)
function increment() {
  count.value [1] 1
}
</script>

Drag options to blanks, or click blank then click option'

A/=

B-=

C*=

D+=

Attempts:

3 left

💡 Hint

Common Mistakes

Using -= which decreases the value.

Using * or / which multiply or divide instead of adding.

To increase the count by 1, use the += operator on count.value.

3fill in blank

hard

Fix the error in the setup function to correctly return the count variable.

Vue

<script setup>
import { ref } from 'vue'
const count = ref(0)
return [1]
</script>

Drag options to blanks, or click blank then click option'

A{ count }

Bcount

C[ count ]

Dcount.value

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the variable directly instead of inside an object.

Returning the value of count instead of the ref itself.

The setup function should return an object with properties to expose them to the template. Returning { count } exposes the reactive variable properly.

4fill in blank

hard

Fill both blanks to create a reactive object and expose its property in setup.

Vue

<script setup>
import { [1] } from 'vue'
const state = [2]({ count: 0 })
return { state }
</script>

Drag options to blanks, or click blank then click option'

Areactive

Bref

Ccomputed

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using ref instead of reactive for an object.

Importing reactive but using ref in code or vice versa.

The reactive function creates a reactive object. We import and use it to make state reactive.

5fill in blank

hard

Fill all three blanks to create a computed property that doubles count.

Vue

<script setup>
import { ref, [1] } from 'vue'
const count = ref(1)
const double = [2](() => count.value [3] 2)
return { count, double }
</script>

Drag options to blanks, or click blank then click option'

Acomputed

B+

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication to double.

Not importing computed from Vue.

The computed function creates a reactive computed property. To double count, multiply count.value by 2 using *.

Practice

1. What is the main purpose of the setup function in a Vue 3 component?

easy

A. To register global components

B. To define reactive data and functions before the component renders

C. To handle routing between pages

D. To style the component using CSS

Solution

1. Step 1: Understand the role of setup in Vue 3

   The setup function is where you declare reactive data and functions that the component will use.

2. Step 2: Compare with other options

   Styling, routing, and global registration are handled elsewhere, not in setup.

3. Final Answer:

   To define reactive data and functions before the component renders -> Option B

4. Quick Check:

   Setup function = reactive data + functions [OK]

Hint: Remember: setup is for data and logic, not styling or routing [OK]

Common Mistakes:

• Confusing setup with styling or routing
• Thinking setup runs after rendering
• Assuming setup registers global components

2. Which of the following is the correct way to declare a reactive variable inside the setup function using Vue 3 Composition API?

easy

A. const count = useState(0);

B. const count = reactive(0);

C. const count = reactive({ value: 0 });

D. const count = ref(0);

Solution

1. Step 1: Identify correct reactive declaration for simple values

   For simple reactive variables like numbers, ref is used, e.g., const count = ref(0);.

2. Step 2: Check other options

   reactive is for objects, not primitives; useState is not a Vue function.

3. Final Answer:

   const count = ref(0); -> Option D

4. Quick Check:

   Simple reactive variable = ref() [OK]

Hint: Use ref() for single values, reactive() for objects [OK]

Common Mistakes:

• Using reactive() for primitive values
• Trying to use non-existent useState()
• Wrapping primitive in reactive({ value: ... }) unnecessarily

3. Consider this Vue 3 component setup code:

import { ref } from 'vue';

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

What will be the value of message after calling update()?

medium

A. 'Hi'

B. undefined

C. 'Hello'

D. An error occurs

Solution

1. Step 1: Understand ref and updating its value

   message is a ref holding 'Hello'. Calling update() sets message.value to 'Hi'.

2. Step 2: Determine final value after update

   After update(), message.value is 'Hi', so message reactive variable reflects 'Hi'.

3. Final Answer:

   'Hi' -> Option A

4. Quick Check:

   Ref value updated correctly = 'Hi' [OK]

Hint: Remember to access .value to update ref variables [OK]

Common Mistakes:

• Forgetting to use .value to update ref
• Assuming message itself changes, not message.value
• Thinking update() does not affect message

4. Identify the error in this Vue 3 setup function:

import { ref } from 'vue';

export default {
  setup() {
    const count = ref(0);
    function increment() {
      count = count + 1;
    }
    return { count, increment };
  }
}

medium

A. setup function should return a single object

B. Missing import of reactive

C. Cannot assign to ref variable directly; should use count.value

D. increment function is not declared correctly

Solution

1. Step 1: Check how ref variables are updated

   Ref variables hold their value inside .value. Direct assignment like count = count + 1 is invalid.

2. Step 2: Correct way to update ref

   Use count.value = count.value + 1 or count.value++ to update.

3. Final Answer:

   Cannot assign to ref variable directly; should use count.value -> Option C

4. Quick Check:

   Update ref with .value [OK]

Hint: Always update ref with .value, not direct assignment [OK]

Common Mistakes:

• Assigning directly to ref variable
• Forgetting to use .value when updating
• Confusing reactive and ref update syntax

5. You want to create a Vue 3 component using <script setup> that has a reactive object with properties name and age. Which code correctly defines this reactive object and updates age by 1 inside setup?

hard

A. import { reactive } from 'vue';

const person = reactive({ name: 'Alice', age: 30 });
person.age++;

B. import { ref } from 'vue';

const person = ref({ name: 'Alice', age: 30 });
person.age++;

C. import { reactive } from 'vue';

const person = reactive({ name: 'Alice', age: 30 });
person = { ...person, age: person.age + 1 };

D. import { ref } from 'vue';

const person = ref({ name: 'Alice', age: 30 });
person.value.age = person.age + 1;

Solution

1. Step 1: Choose correct reactive type for object

   Use reactive for objects to make all properties reactive.

2. Step 2: Update property correctly

   With reactive, update properties directly like person.age++. Using ref with objects requires accessing .value.

3. Final Answer:

   import { reactive } from 'vue'; const person = reactive({ name: 'Alice', age: 30 }); person.age++; -> Option A

4. Quick Check:

   Reactive object updated directly =

   import { reactive } from 'vue';
   
   const person = reactive({ name: 'Alice', age: 30 });
   person.age++;
   

   [OK]

Hint: Use reactive() for objects, update properties directly [OK]

Common Mistakes:

• Using ref for objects without .value access
• Reassigning reactive object instead of updating property
• Trying to increment property on ref object without .value