v-model with checkboxes in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does v-model do when used with a single checkbox in Vue?

v-model binds the checkbox's checked state to a data property. When the checkbox is checked, the property becomes true. When unchecked, it becomes false.

beginner

How does v-model work with multiple checkboxes bound to the same array?

Each checked checkbox adds its value to the array. Unchecking removes its value. This way, the array always holds the selected checkbox values.

beginner

What type of data should the bound variable be when using v-model with multiple checkboxes?

The bound variable should be an array to hold multiple selected values from the checkboxes.

intermediate

How do you set the value each checkbox adds to the array when using v-model with multiple checkboxes?

Use the value attribute on each checkbox input to specify what value it adds to the array when checked.

intermediate

What happens if you bind v-model to a non-array variable with multiple checkboxes?

Vue will not be able to track multiple selections properly. The bound variable should be an array to handle multiple checkbox values.

What type of data should v-model bind to when using multiple checkboxes?

A An array

B A boolean

C A string

D A number

Multiple checkboxes represent multiple selections, so v-model binds to an array holding all selected values.

What does v-model bind to for a single checkbox?

A An array

B A number

C An object

D A boolean

A single checkbox toggles between checked and unchecked, so v-model binds to a boolean value.

How do you specify the value a checkbox adds to the array when checked?

A Using the <code>checked</code> attribute

B Using the <code>value</code> attribute

C Using the <code>name</code> attribute

D Using the <code>id</code> attribute

The value attribute sets what value the checkbox adds to the array when checked.

What happens if you uncheck a checkbox bound with v-model to an array?

A Its value is removed from the array

B Its value stays in the array

C The array becomes empty

D The array becomes a boolean

Unchecking removes that checkbox's value from the array, keeping the array updated with only selected values.

Which Vue directive is used to bind checkbox state to data?

A <code>v-bind</code>

B <code>v-if</code>

C <code>v-model</code>

D <code>v-for</code>

v-model creates two-way binding between form inputs like checkboxes and Vue data.

Explain how v-model works with multiple checkboxes in Vue.

Think about how multiple selections are stored and updated.

Describe the difference in v-model usage between a single checkbox and multiple checkboxes.

Consider the data type that matches the selection type.

Practice

1. What type of data should you use with v-model when binding to multiple checkboxes in Vue?

easy

A. A string representing the last selected checkbox

B. A boolean to represent true or false

C. An array to hold the selected values

D. A number counting how many checkboxes are checked

Solution

1. Step 1: Understand checkbox binding

   When multiple checkboxes are bound with v-model, Vue expects an array to store all selected values.

2. Step 2: Compare data types for checkboxes

   A boolean is used for single checkboxes, but for multiple checkboxes, an array collects all checked values.

3. Final Answer:

   An array to hold the selected values -> Option C

4. Quick Check:

   Multiple checkboxes = array [OK]

Hint: Multiple checkboxes always bind to an array [OK]

Common Mistakes:

• Using a boolean for multiple checkboxes
• Binding to a string instead of an array
• Expecting a number to track checked boxes

2. Which of the following is the correct syntax to bind a single checkbox with v-model in Vue?

easy

A. <input type='checkbox' v-model='checked' />

B. <input type='checkbox' :value='checked' />

C. <input type='checkbox' v-bind='checked' />

D. <input type='checkbox' v-model:value='checked' />

Solution

1. Step 1: Identify correct binding directive

   The v-model directive binds the checkbox's checked state to a data property.

2. Step 2: Check syntax correctness

   <input type='checkbox' v-model='checked' /> uses v-model='checked' which is the correct and simplest syntax for binding a single checkbox.

3. Final Answer:

   <input type='checkbox' v-model='checked' /> -> Option A

4. Quick Check:

   Single checkbox uses v-model='property' [OK]

Hint: Use v-model directly on checkbox for single binding [OK]

Common Mistakes:

• Using :value instead of v-model
• Using v-bind without specifying property
• Using v-model:value which is invalid

3. Given this Vue template code:

<template>
  <input type='checkbox' v-model='selected' value='apple' />
  <input type='checkbox' v-model='selected' value='banana' />
  <input type='checkbox' v-model='selected' value='cherry' />
  <p>Selected: {{ selected }}</p>
</template>

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

What will be displayed after the user checks the boxes for "apple" and "cherry"?

medium

A. Selected: 'apple,cherry'

B. Selected: ['apple', 'cherry']

C. Selected: ['apple']

D. Selected: true

Solution

1. Step 1: Understand v-model with multiple checkboxes

   When multiple checkboxes share the same v-model bound to an array, Vue adds the checkbox's value to the array when checked.

2. Step 2: Check which boxes are selected

   User checked "apple" and "cherry", so the array contains ['apple', 'cherry'].

3. Final Answer:

   Selected: ['apple', 'cherry'] -> Option B

4. Quick Check:

   Checked boxes values collected in array [OK]

Hint: Multiple checkboxes with same v-model store values in array [OK]

Common Mistakes:

• Expecting a string instead of an array
• Thinking only last checked value is stored
• Confusing boolean with array for multiple checkboxes

4. What is wrong with this Vue checkbox binding?

<input type='checkbox' v-model='checked' value='yes' />

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

Why does checking the box not add 'yes' to checked?

medium

A. Because checked should be a string, not boolean

B. Because value attribute is missing

C. Because v-model cannot be used on checkboxes

D. Because checked is a boolean, not an array, so value is ignored

Solution

1. Step 1: Identify data type for v-model

   The variable checked is a boolean, so Vue treats the checkbox as a single toggle (true/false).

2. Step 2: Understand effect of value attribute

   When v-model is boolean, the value attribute is ignored; it only matters when binding to an array.

3. Final Answer:

   Because checked is a boolean, not an array, so value is ignored -> Option D

4. Quick Check:

   Boolean v-model ignores value attribute [OK]

Hint: Boolean v-model ignores value; use array for multiple values [OK]

Common Mistakes:

• Thinking value attribute always affects checkbox state
• Believing v-model can't be used on checkboxes
• Using string instead of boolean or array incorrectly

5. You want to create a group of checkboxes for selecting favorite fruits using v-model. The data property is favorites initialized as an empty array. Which code snippet correctly updates favorites when users check or uncheck fruits?

hard

A. <input type='checkbox' v-model='favorites' value='apple' />
<input type='checkbox' v-model='favorites' value='banana' />
<input type='checkbox' v-model='favorites' value='cherry' />

B. <input type='checkbox' v-model='favorites' :value='true' />
<input type='checkbox' v-model='favorites' :value='false' />

C. <input type='checkbox' v-model='favorites.apple' />
<input type='checkbox' v-model='favorites.banana' />

D. <input type='checkbox' v-model='favorites' value='true' />
<input type='checkbox' v-model='favorites' value='false' />

Solution

1. Step 1: Understand array binding for multiple checkboxes

   Binding multiple checkboxes to the same array with v-model and distinct value attributes collects checked values in the array.

2. Step 2: Evaluate each option's correctness

   <input type='checkbox' v-model='favorites' value='apple' /> <input type='checkbox' v-model='favorites' value='banana' /> <input type='checkbox' v-model='favorites' value='cherry' /> correctly uses v-model='favorites' with unique string values for each checkbox, so checked fruits are added or removed from the array.

3. Final Answer:

   <input type='checkbox' v-model='favorites' value='apple' /> <input type='checkbox' v-model='favorites' value='banana' /> <input type='checkbox' v-model='favorites' value='cherry' /> -> Option A

4. Quick Check:

   Multiple checkboxes + array + unique values = correct binding [OK]

Hint: Use array with unique values for multiple checkboxes [OK]

Common Mistakes:

• Using boolean values instead of unique strings
• Binding to object properties instead of array
• Using same value for all checkboxes