Prop types and validation in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a prop named title of type String.

Vue

<script setup>
const props = defineProps({
  title: [1]
})
</script>

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

AArray

BNumber

CBoolean

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong type like Number for a text prop.

Not declaring the prop at all.

The title prop should be declared with type String to accept text values.

2fill in blank

medium

Complete the code to make the count prop required and of type Number.

Vue

<script setup>
const props = defineProps({
  count: { type: [1], required: true }
})
</script>

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

ANumber

BString

CBoolean

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to set required: true.

Using the wrong type for the prop.

The count prop must be a Number and is marked as required.

3fill in blank

hard

Fix the error in the prop validation by completing the validator function to accept only even numbers.

Vue

<script setup>
const props = defineProps({
  evenNumber: {
    type: Number,
    validator: value => value [1] 2 === 0
  }
})
</script>

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

A%

B===

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using === instead of % for the check.

Not returning a boolean from the validator.

The modulo operator % checks if the number is divisible by 2 with no remainder, meaning it is even.

4fill in blank

hard

Fill both blanks to declare a status prop with type String and a default value of 'active'.

Vue

<script setup>
const props = defineProps({
  status: { type: [1], default: [2] }
})
</script>

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

AString

B'inactive'

C'active'

DBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using a Boolean type instead of String.

Setting the wrong default value.

The status prop is a String and defaults to 'active' if not provided.

5fill in blank

hard

Fill all three blanks to declare a user prop as an Object with required true and a validator that checks if it has a name property.

Vue

<script setup>
const props = defineProps({
  user: {
    type: [1],
    required: [2],
    validator: obj => obj && typeof obj.name === [3]
  }
})
</script>

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

AObject

Btrue

C'string'

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting required to false or forgetting it.

Using wrong type for the validator check.

The user prop is an Object, required, and the validator checks if name is a string.

Practice

1. What is the main purpose of defining props with types in a Vue component?

easy

A. To ensure the component receives data in the expected format

B. To style the component automatically

C. To make the component load faster

D. To prevent the component from rendering

Solution

1. Step 1: Understand what props do in Vue

   Props allow passing data from a parent to a child component.

2. Step 2: Recognize the role of prop types

   Defining types helps Vue check if the data matches the expected format, catching errors early.

3. Final Answer:

   To ensure the component receives data in the expected format -> Option A

4. Quick Check:

   Prop types = data format check [OK]

Hint: Prop types check data format passed to components [OK]

Common Mistakes:

• Thinking prop types affect styling
• Believing prop types improve speed
• Assuming prop types stop rendering

2. Which of the following is the correct syntax to define a required string prop named title in a Vue component?

easy

A. props: { title: String, required: true }

B. props: { title: { type: String, required: true } }

C. props: { title: { required: true type: String } }

D. props: { title: { String, required: true } }

Solution

1. Step 1: Recall Vue prop syntax for validation

   Props with validation use an object with keys like type and required.

2. Step 2: Check the correct order and structure

   The correct syntax is { type: String, required: true } inside the prop definition.

3. Final Answer:

   props: { title: { type: String, required: true } } -> Option B

4. Quick Check:

   Prop validation uses object with type and required [OK]

Hint: Use object with type and required keys for prop validation [OK]

Common Mistakes:

• Placing required outside the prop object
• Using array instead of object for validation
• Wrong order or missing keys in prop definition

3. Given this Vue component prop definition:

props: { count: { type: Number, default: 0 } }

What will be the value of count inside the component if the parent does NOT pass any count prop?

medium

A. 0

B. null

C. undefined

D. NaN

Solution

1. Step 1: Understand default prop values

   If a prop is not passed, Vue uses the default value if defined.

2. Step 2: Check the default value for count

   The default is set to 0, so count will be 0 inside the component.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Missing prop uses default value [OK]

Hint: Default prop value used if parent omits prop [OK]

Common Mistakes:

• Assuming undefined if prop is missing
• Confusing null with default value
• Expecting error when prop is missing

4. Consider this prop validation in a Vue component:

props: { age: { type: Number, required: true } }

What will happen if the parent passes age="twenty" (a string) instead of a number?

medium

A. Vue will automatically convert the string to a number

B. Vue will throw a runtime error and stop rendering

C. Vue will show a console warning about the type mismatch

D. Vue will ignore the prop and use the default value

Solution

1. Step 1: Understand Vue's prop type checking behavior

   Vue checks prop types and warns in the console if types don't match but does not stop rendering.

2. Step 2: Check what happens with wrong type

   Passing a string instead of a number triggers a console warning but no error or conversion.

3. Final Answer:

   Vue will show a console warning about the type mismatch -> Option C

4. Quick Check:

   Wrong prop type triggers warning, not error [OK]

Hint: Vue warns on wrong prop types but keeps rendering [OK]

Common Mistakes:

• Expecting runtime errors instead of warnings
• Thinking Vue auto-converts prop types
• Assuming default value is used on type mismatch

5. You want to validate a prop status that only accepts the strings 'active', 'inactive', or 'pending'. Which is the correct way to add this validation in Vue?

hard

A. props: { status: { type: String, validate: value => ['active', 'inactive', 'pending'].includes(value) } }"

B. props: { status: { type: String, required: true, default: 'active' } }

C. props: { status: { type: String, enum: ['active', 'inactive', 'pending'] } }

D. props: { status: { type: String, validator: value => ['active', 'inactive', 'pending'].includes(value) } }

Solution

1. Step 1: Recall how to restrict prop values in Vue

   Vue uses a validator function to check if a prop value is allowed.

2. Step 2: Check the correct validator syntax

   The validator is a function returning true if the value is valid, like value => ['active', 'inactive', 'pending'].includes(value).

3. Final Answer:

   props: { status: { type: String, validator: value => ['active', 'inactive', 'pending'].includes(value) } } -> Option D

4. Quick Check:

   Use validator function to restrict prop values [OK]

Hint: Use validator function to limit allowed prop values [OK]

Common Mistakes:

• Using non-existent 'enum' key for props
• Confusing 'validate' with 'validator'
• Relying only on default or required without value check