Ref and reactive in Composition API in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a reactive reference for a count variable.

Vue

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

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

Areactive

Bref

Ccomputed

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using reactive instead of ref for primitive values.

Forgetting to import ref from 'vue'.

The ref function creates a reactive reference to a value, perfect for primitive types like numbers.

2fill in blank

medium

Complete the code to create a reactive object with a name property.

Vue

<script setup>
import { reactive } from 'vue'
const user = reactive({ [1]: 'Alice' })
</script>

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

Aage

Bvalue

Ccount

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name unrelated to the user's name.

Trying to use ref instead of reactive for an object.

The reactive function wraps an object to make all its properties reactive. Here, name is the property we want.

3fill in blank

hard

Fix the error in accessing the value of a ref variable in the template.

Vue

<template>
  <p>Count is: {{ [1] }}</p>
</template>

<script setup>
import { ref } from 'vue'
const count = ref(5)
</script>

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

Acount

Bcount.value

Ccount()

Dvalue.count

Attempts:

3 left

💡 Hint

Common Mistakes

Using .value inside the template, which is unnecessary.

Trying to call the ref as a function.

In Vue templates, you can use a ref variable directly without .value. Vue unwraps it automatically.

4fill in blank

hard

Fill both blanks to create a reactive object and update its property.

Vue

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

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

Areactive

Bref

Ccomputed

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing ref and reactive incorrectly.

Forgetting to import reactive.

reactive is used to create a reactive object. We import and call reactive to wrap the object.

5fill in blank

hard

Fill all three blanks to create a ref, update its value, and display it in the template.

Vue

<template>
  <p>Message: {{ [1] }}</p>
</template>

<script setup>
import { [2] } from 'vue'
const message = [3]('Hello')
message.value = 'Hi there!'
</script>

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

Amessage

Bref

Cmessage.value

Dreactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using message.value in the template.

Importing reactive instead of ref.

Using reactive to create a primitive ref.

We import ref to create a reactive reference. The variable message holds the ref. In the template, we use message directly because Vue unwraps refs automatically.

Practice

1. In Vue's Composition API, what is the main difference between ref and reactive?

easy

A. ref is used to create components, reactive is used to create directives.

B. ref is only for arrays, reactive is only for strings.

C. ref is for simple values accessed with .value, reactive is for objects and arrays accessed directly.

D. ref and reactive are exactly the same and can be used interchangeably.

Solution

1. Step 1: Understand ref usage

   ref holds simple reactive values like numbers or strings and requires accessing the value with .value.

2. Step 2: Understand reactive usage

   reactive wraps objects or arrays to make their properties reactive and accessed directly without .value.

3. Final Answer:

   ref is for simple values accessed with .value, reactive is for objects and arrays accessed directly. -> Option C

4. Quick Check:

   ref vs reactive difference = D [OK]

Hint: Remember: ref = simple value with .value, reactive = object direct access [OK]

Common Mistakes:

• Thinking ref works directly on objects without .value
• Confusing reactive as only for primitive values
• Assuming ref and reactive are interchangeable

2. Which of the following is the correct way to declare a reactive object in Vue 3 Composition API?

easy

A. const state = ref({ count: 0 })

B. const state = reactive({ count: 0 })

C. const state = reactive(0)

D. const state = ref(0)

Solution

1. Step 1: Identify correct reactive syntax for objects

   reactive is used to wrap objects to make their properties reactive.

2. Step 2: Check each option

   const state = ref({ count: 0 }) uses ref with an object, which is allowed but requires .value to access. const state = reactive({ count: 0 }) correctly uses reactive with an object. const state = reactive(0) uses reactive with a number, which is invalid. const state = ref(0) uses ref with a number, which is valid but not for objects.

3. Final Answer:

   const state = reactive({ count: 0 }) -> Option B

4. Quick Check:

   reactive object syntax = C [OK]

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

Common Mistakes:

• Using reactive() on primitive values
• Using ref() for objects without .value access
• Confusing reactive and ref usage

3. Given the code:

import { ref, reactive } from 'vue';
const count = ref(0);
const state = reactive({ clicks: 0 });

count.value++;
state.clicks++;

console.log(count.value, state.clicks);

What will be logged to the console?

medium

A. 0 1

B. 0 0

C. 1 0

D. 1 1

Solution

1. Step 1: Understand ref and reactive increments

   count is a ref holding 0, incremented by count.value++ to 1. state is reactive object with clicks 0, incremented by state.clicks++ to 1.

2. Step 2: Check console.log output

   Logging count.value and state.clicks will print 1 1.

3. Final Answer:

   1 1 -> Option D

4. Quick Check:

   Increment ref and reactive values = A [OK]

Hint: Increment ref with .value, reactive directly [OK]

Common Mistakes:

• Forgetting to use .value with ref
• Assuming reactive needs .value
• Mixing up initial values

4. What is wrong with this Vue Composition API code?

import { ref } from 'vue';
const user = ref({ name: 'Alice' });
user.name = 'Bob';

medium

A. You must use user.value.name to update the name property.

B. ref cannot hold objects, use reactive instead.

C. You should use user.value() to access the object.

D. There is no error; the code works fine.

Solution

1. Step 1: Understand ref with objects

   ref wraps the object, so to access or update properties inside, you must use .value.

2. Step 2: Identify the error in property update

   The code tries to update user.name directly, which is incorrect. It should be user.value.name.

3. Final Answer:

   You must use user.value.name to update the name property. -> Option A

4. Quick Check:

   Access ref object properties with .value = A [OK]

Hint: Use .value to access or update ref object properties [OK]

Common Mistakes:

• Accessing ref object properties without .value
• Confusing ref and reactive usage
• Thinking ref cannot hold objects

5. You want to create a reactive state for a form with fields name (string) and tags (array). You also want to track a simple counter for submissions. Which setup correctly uses ref and reactive together?

hard

A. const form = reactive({ name: '', tags: [] }); const submitCount = ref(0);

B. const form = ref({ name: '', tags: [] }); const submitCount = reactive(0);

C. const form = reactive(''); const submitCount = ref([]);

D. const form = ref(''); const submitCount = reactive({ count: 0 });

Solution

1. Step 1: Identify correct usage for form object

   The form has multiple fields, so reactive is best to wrap the object with name and tags properties.

2. Step 2: Identify correct usage for simple counter

   The submission count is a simple number, so ref is appropriate to track it reactively.

3. Final Answer:

   const form = reactive({ name: '', tags: [] }); const submitCount = ref(0); -> Option A

4. Quick Check:

   Use reactive for objects, ref for simple values = B [OK]

Hint: Use reactive for objects/arrays, ref for simple values [OK]

Common Mistakes:

• Using ref for complex objects without .value
• Using reactive on primitive values
• Mixing up which data needs ref or reactive