Reactive data with ref 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 = ref(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 a primitive value.

Trying to import a function that doesn't exist.

The ref function creates a reactive reference to a value, allowing Vue to track changes.

2fill in blank

medium

Complete the template to display the reactive count value.

Vue

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

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

Acount

Bcount.value()

Ccount()

Dcount.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using count without .value in the template.

Trying to call count as a function.

When using ref, you access the actual value with .value.

3fill in blank

hard

Fix the error in updating the reactive count value inside a method.

Vue

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

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

A+=

B++

C-=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using ++ directly on count without .value.

Using = instead of += causing overwrite.

To update the value inside a ref, use count.value += 1. The blank is for the operator between count.value and 1.

4fill in blank

hard

Fill both blanks to correctly update the reactive count value by 1.

Vue

<script setup>
import { ref } from 'vue'
const count = ref(0)
function increment() {
  count[1] [2] 1
}
</script>

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

A.value

B+=

C-=

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use .value.

Using ++ operator incorrectly on ref.

You must access count.value to update the inner value, then use += to add 1.

5fill in blank

hard

Fill all three blanks to create a reactive count, display it, and update it on button click.

Vue

<template>
  <p>Count: {{ [1] }}</p>
  <button @click="[2]">Add 1</button>
</template>

<script setup>
import { ref } from 'vue'
const count = ref(0)
function [2]() {
  count[3] 1
}
</script>

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

Acount.value

Bincrement

C+=

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using count instead of count.value in template.

Mismatch between function name in template and script.

Forgetting to use .value when updating.

The template shows count.value to display the reactive value. The button calls the increment function, which updates count.value += 1.

Practice

1. What does the ref function in Vue do?

easy

A. Defines a new component

B. Creates a reactive data reference that Vue tracks for changes

C. Imports external libraries

D. Sets up routing between pages

Solution

1. Step 1: Understand the purpose of ref

   ref is used to create reactive data that Vue can track and update the UI when it changes.

2. Step 2: Compare options with ref usage

   Options A, C, and D describe unrelated Vue features like components, imports, and routing, not reactive data.

3. Final Answer:

   Creates a reactive data reference that Vue tracks for changes -> Option B

4. Quick Check:

   ref creates reactive data = B [OK]

Hint: Remember: ref makes data reactive for UI updates [OK]

Common Mistakes:

• Confusing ref with component creation
• Thinking ref imports libraries
• Mixing ref with routing setup

2. Which is the correct way to declare a reactive variable count initialized to 0 using ref in Vue?

easy

A. var count = ref;

B. const count = reactive(0);

C. const count = ref(0);

D. let count = ref = 0;

Solution

1. Step 1: Recall correct ref syntax

   The correct syntax is const count = ref(0); to create a reactive reference with initial value 0.

2. Step 2: Identify incorrect options

   const count = reactive(0); uses reactive incorrectly with a primitive. let count = ref = 0; has invalid assignment syntax. var count = ref; incorrectly assigns the ref function without calling it and uses var which is discouraged in modern Vue code.

3. Final Answer:

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

4. Quick Check:

   Use const with ref() for reactive variables = D [OK]

Hint: Use const and call ref() with initial value [OK]

Common Mistakes:

• Using reactive() for primitives
• Incorrect assignment syntax
• Using var instead of const

3. Given the code:

import { ref } from 'vue';
const count = ref(5);
count.value++;
console.log(count.value);

What will be logged to the console?

medium

A. 6

B. 5

C. undefined

D. Error: count is not a function

Solution

1. Step 1: Understand ref and .value usage

   count is a reactive reference initialized to 5. Incrementing count.value++ increases it to 6.

2. Step 2: Determine console output

   Logging count.value after increment prints 6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Increment ref.value updates value = 6 [OK]

Hint: Remember to use .value to access and update ref data [OK]

Common Mistakes:

• Logging count instead of count.value
• Forgetting to use .value to update
• Expecting original value without increment

4. What is wrong with this Vue code snippet?

import { ref } from 'vue';
const message = ref('Hello');
message = 'Hi';

medium

A. You cannot reassign a ref variable directly; must update .value

B. ref cannot hold string values

C. Missing parentheses when calling ref

D. No import statement for ref

Solution

1. Step 1: Identify how to update ref values

   Ref variables are constants holding reactive objects. You cannot reassign the variable itself; instead, update the inner value with message.value = 'Hi';.

2. Step 2: Check other options

   ref cannot hold string values is false because ref can hold strings. Missing parentheses when calling ref is false because ref is called correctly. No import statement for ref is false because import is present.

3. Final Answer:

   You cannot reassign a ref variable directly; must update .value -> Option A

4. Quick Check:

   Update ref.value, not ref variable = C [OK]

Hint: Change .value property, not the ref variable itself [OK]

Common Mistakes:

• Reassigning ref variable instead of .value
• Thinking ref can't hold strings
• Missing import statement

5. You want to create a reactive counter that increments only if the current count is less than 10. Which Vue code correctly implements this using ref?

hard

A. let count = ref(0);
if (count.value <= 10) {
count.value += 1;
}

B. const count = ref(0);
if (count < 10) {
count++;
}

C. const count = reactive(0);
if (count.value < 10) {
count.value++;
}

D. const count = ref(0);
if (count.value < 10) {
count.value++;
}

Solution

1. Step 1: Use ref and access .value correctly

   const count = ref(0); if (count.value < 10) { count.value++; } correctly declares count with ref(0) and checks count.value < 10 before incrementing count.value++.

2. Step 2: Identify errors in other options

   const count = ref(0); if (count < 10) { count++; } incorrectly compares and increments count without .value. const count = reactive(0); if (count.value < 10) { count.value++; } uses reactive with a primitive, which is incorrect. let count = ref(0); if (count.value <= 10) { count.value += 1; } uses let (allowed but less preferred) and checks <= 10, which allows increment at 10, violating the condition.

3. Final Answer:

   const count = ref(0); if (count.value < 10) { count.value++; } -> Option D

4. Quick Check:

   Use ref with .value and correct condition = A [OK]

Hint: Always use .value to read and write ref data [OK]

Common Mistakes:

• Forgetting .value when reading or writing
• Using reactive() for primitives
• Incorrect comparison operators