Custom v-model on components in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind the custom model value using v-model.

Vue

<template>
  <input type="text" v-model=[1] />
</template>

<script setup>
const props = defineProps({
  modelValue: String
})
</script>

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

A"text"

B"value"

C"inputValue"

D"modelValue"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a prop name other than 'modelValue' without customizing v-model.

Trying to bind v-model to a non-existent prop.

The v-model directive by default binds to the modelValue prop in Vue 3 custom components.

2fill in blank

medium

Complete the code to emit the update event for the custom v-model.

Vue

<script setup>
const emit = defineEmits([[1]])
</script>

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

A"change"

B"input"

C"update:modelValue"

D"update:value"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'input' event instead of 'update:modelValue'.

Using 'update:value' when the prop is 'modelValue'.

Vue 3 custom v-model uses the event name update:modelValue to update the parent component.

3fill in blank

hard

Fix the error in emitting the update event with the new value.

Vue

<script setup>
const emit = defineEmits(["update:modelValue"])

function onInput(event) {
  emit([1], event.target.value)
}
</script>

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

A"input"

B"update:modelValue"

C"change"

D"modelValue"

Attempts:

3 left

💡 Hint

Common Mistakes

Emitting 'input' event instead of 'update:modelValue'.

Using the prop name as event name without 'update:' prefix.

The event emitted to update the v-model must be exactly update:modelValue.

4fill in blank

hard

Fill both blanks to customize v-model with a different prop and event name.

Vue

<script setup>
const props = defineProps({
  [1]: String
})
const emit = defineEmits([[2]])
</script>

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

A"checkedValue"

B"update:checkedValue"

C"modelValue"

D"update:modelValue"

Attempts:

3 left

💡 Hint

Common Mistakes

Using mismatched prop and event names.

Not prefixing event name with 'update:'.

To customize v-model, you define a different prop and matching update event name.

5fill in blank

hard

Fill all three blanks to implement a custom v-model with a checkbox input.

Vue

<template>
  <input type="checkbox" :checked=[1] @change="event => emit([2], event.target.checked)" />
</template>

<script setup>
const props = defineProps({
  [3]: Boolean
})
const emit = defineEmits(["update:isChecked"])
</script>

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

AisChecked

B"update:isChecked"

CisCheckedValue

D"update:isCheckedValue"

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for prop and event.

Not binding the checkbox checked attribute to the prop.

The prop and event names must match for the custom v-model to work. The checkbox's checked state binds to the prop.

Practice

1. What is the default prop name used in a Vue component to work with v-model?

easy

A. inputValue

B. value

C. vModel

D. modelValue

Solution

1. Step 1: Understand Vue's default v-model prop

   Vue uses modelValue as the default prop name to bind data from parent to child.

2. Step 2: Recall the default event name

   The event emitted to update the parent is update:modelValue, matching the prop name.

3. Final Answer:

   modelValue -> Option D

4. Quick Check:

   Default prop for v-model = modelValue [OK]

Hint: Default v-model prop is always 'modelValue' [OK]

Common Mistakes:

• Using 'value' as default prop
• Confusing event name with prop name
• Assuming 'vModel' is default prop

2. Which of the following is the correct syntax to use a custom v-model named checked on a component?

easy

A. <MyCheckbox v-model:checked="isChecked" />

B. <MyCheckbox v-model.checked="isChecked" />

C. <MyCheckbox v-model_checked="isChecked" />

D. <MyCheckbox v-modelChecked="isChecked" />

Solution

1. Step 1: Recall custom v-model syntax

   Vue uses v-model:customName syntax to bind custom model names.

2. Step 2: Match syntax with options

   Only <MyCheckbox v-model:checked="isChecked" /> uses the correct colon syntax for custom v-model binding.

3. Final Answer:

   <MyCheckbox v-model:checked="isChecked" /> -> Option A

4. Quick Check:

   Custom v-model uses colon syntax [OK]

Hint: Use colon for custom v-model names: v-model:customName [OK]

Common Mistakes:

• Using dot instead of colon
• Using underscore instead of colon
• Using camelCase without colon

3. Given this child component code:

props: ['modelValue'],
methods: {
  updateValue(val) {
    this.$emit('update:modelValue', val)
  }
}

And parent usage:

<ChildComponent v-model="parentData" />

What happens when updateValue('new') is called inside the child?

medium

A. The child's modelValue prop changes to 'new'.

B. Nothing happens because event name is wrong.

C. The parent's parentData updates to 'new'.

D. An error occurs because updateValue is not defined.

Solution

1. Step 1: Understand event emission in child

   The child emits update:modelValue with the new value, which Vue listens to for v-model updates.

2. Step 2: Effect on parent data

   The parent bound to v-model receives the event and updates parentData to 'new'.

3. Final Answer:

   The parent's parentData updates to 'new'. -> Option C

4. Quick Check:

   Child emits update:modelValue -> parent updates [OK]

Hint: Child emits update:modelValue event to update parent data [OK]

Common Mistakes:

• Thinking prop changes inside child
• Confusing event name with prop name
• Assuming no update without v-model modifier

4. Identify the error in this child component code for custom v-model named checked:

props: ['checked'],
methods: {
  updateChecked(val) {
    this.$emit('update:checked', val)
  }
}

Parent uses:

<MyCheckbox v-model:checked="isChecked" />

medium

A. Event name should be update:modelValue for custom v-model.

B. Prop name and event name are correct for custom v-model checked.

C. Prop name should be modelValue instead of checked.

D. The method should emit checked event, not update:checked.

Solution

1. Step 1: Check prop and event names for custom v-model

   For v-model:checked, the prop must be checked and event update:checked.

2. Step 2: Verify code matches custom v-model pattern

   The code uses props: ['checked'] and emits update:checked, which is correct.

3. Final Answer:

   Prop name and event name are correct for custom v-model checked. -> Option B

4. Quick Check:

   Custom v-model uses matching prop and update:event [OK]

Hint: Custom v-model uses prop and event names matching the model name [OK]

Common Mistakes:

• Using default modelValue prop for custom v-model
• Emitting wrong event name
• Confusing event and prop names

5. You want to create a component ToggleSwitch that uses a custom v-model named active. Which of these code snippets correctly implements the child component's props and emits to support this?

hard

A. props: ['active'],
methods: {
toggle() {
this.$emit('update:active', !this.active)
}
}

B. props: ['modelValue'],
methods: {
toggle() {
this.$emit('update:modelValue', !this.modelValue)
}
}

C. props: ['active'],
methods: {
toggle() {
this.$emit('update:modelValue', !this.active)
}
}

D. props: ['modelValue'],
methods: {
toggle() {
this.$emit('update:active', !this.modelValue)
}
}

Solution

1. Step 1: Match prop and event names to custom v-model name

   For v-model:active, the prop must be active and event update:active.

2. Step 2: Check each option for correct prop and event

   props: ['active'],
   methods: {
     toggle() {
       this.$emit('update:active', !this.active)
     }
   }

   uses props: ['active'] and emits update:active, matching the custom v-model name.

3. Final Answer:

   props: ['active'], methods: { toggle() { this.$emit('update:active', !this.active) } } -> Option A

4. Quick Check:

   Custom v-model prop and event must match model name [OK]

Hint: Custom v-model prop and event must match the model name exactly [OK]

Common Mistakes:

• Mixing default modelValue with custom names
• Emitting wrong event name
• Using wrong prop name for custom v-model