Computed with getter and setter in Vue

Introduction

Computed properties with getter and setter let you create values that update automatically and can also change other data when you set them.

You want to show a value based on other data but also let users change it.

You need to format or combine data for display and update the original data when edited.

You want to keep your template simple by using computed properties instead of methods.

You want to react to changes in a value and update related data automatically.

Syntax

Vue

computed: {
  propertyName: {
    get() {
      // return a value based on other data
    },
    set(newValue) {
      // update other data based on newValue
    }
  }
}

The get function returns the computed value.

The set function runs when you assign a new value to the computed property.

Examples

This example combines first and last names and updates them when fullName changes.

Vue

computed: {
  fullName: {
    get() {
      return this.firstName + ' ' + this.lastName;
    },
    set(value) {
      const parts = value.split(' ');
      this.firstName = parts[0];
      this.lastName = parts.slice(1).join(' ') || '';
    }
  }
}

This example reverses a message string and updates the original message when reversedMessage changes.

Vue

computed: {
  reversedMessage: {
    get() {
      return this.message.split('').reverse().join('');
    },
    set(value) {
      this.message = value.split('').reverse().join('');
    }
  }
}

Sample Program

This Vue component shows an input bound to a computed property with getter and setter. Changing the input updates first and last names separately. The paragraphs show the current first and last names.

Vue

<template>
  <div>
    <input v-model="fullName" aria-label="Full name input" />
    <p>Your first name is: {{ firstName }}</p>
    <p>Your last name is: {{ lastName }}</p>
  </div>
</template>

<script setup>
import { ref, computed } from 'vue'

const firstName = ref('John')
const lastName = ref('Doe')

const fullName = computed({
  get() {
    return `${firstName.value} ${lastName.value}`
  },
  set(value) {
    const parts = value.split(' ')
    firstName.value = parts[0] || ''
    lastName.value = parts.slice(1).join(' ') || ''
  }
})
</script>

Important Notes

Computed properties with setters let you create two-way bindings easily.

Always handle cases where the input might not split cleanly to avoid errors.

Use v-model on computed properties with setters for smooth user input.

Summary

Computed properties can have both get and set to read and write values.

This helps keep your data and UI in sync with less code.

Use them to create smart, reactive properties that update other data when changed.

Practice

1.

What is the main purpose of a computed property with both get and set in Vue?

easy

A. To create a reactive property that can both read and update data

B. To define a method that runs only once

C. To store static values that never change

D. To replace the data object entirely

Solution

1. Step 1: Understand computed properties

   Computed properties in Vue are reactive and can automatically update when dependencies change.

2. Step 2: Role of getter and setter

   Using both get and set allows reading the value and updating related data reactively.

3. Final Answer:

   To create a reactive property that can both read and update data -> Option A

4. Quick Check:

   Computed with get/set = reactive read and write [OK]

Hint: Remember: get reads, set writes reactive data [OK]

Common Mistakes:

• Thinking computed properties are static
• Confusing computed with methods
• Believing set is optional for writing data

2.

Which of the following is the correct syntax to define a computed property with a getter and setter in Vue 3 using <script setup>?

const fullName = computed({
  get() {
    return this.firstName + ' ' + this.lastName
  },
  set(value) {
    const names = value.split(' ')
    this.firstName = names[0]
    this.lastName = names[1]
  }
})

easy

A. Use arrow functions for get and set

B. Correct as is

C. Remove set, only get is allowed

D. Use function keyword without commas

Solution

1. Step 1: Check computed property syntax

   Vue 3 allows computed properties with an object containing get and set methods.

2. Step 2: Validate the example code

   The code correctly defines get and set as functions inside an object passed to computed().

3. Final Answer:

   Correct as is -> Option B

4. Quick Check:

   Object with get/set inside computed = correct syntax [OK]

Hint: Use object with get and set functions inside computed() [OK]

Common Mistakes:

• Using arrow functions that break 'this' context
• Omitting commas between get and set
• Trying to define computed as a single function

3.

Given this Vue 3 <script setup> code, what will be the console output after fullName.value = 'Jane Doe'?

import { ref, computed } from 'vue'

const firstName = ref('John')
const lastName = ref('Smith')

const fullName = computed({
  get() {
    return firstName.value + ' ' + lastName.value
  },
  set(value) {
    const names = value.split(' ')
    firstName.value = names[0]
    lastName.value = names[1]
  }
})

fullName.value = 'Jane Doe'
console.log(firstName.value, lastName.value)

medium

A. 'Jane Doe' 'Doe'

B. Error: Cannot assign to computed property

C. 'Jane' 'Doe'

D. 'John' 'Smith'

Solution

1. Step 1: Understand the setter logic

   Setting fullName.value splits the string into ['Jane', 'Doe'] and assigns to firstName.value and lastName.value.

2. Step 2: Check console.log output

   After assignment, firstName.value is 'Jane' and lastName.value is 'Doe', so console logs 'Jane Doe'.

3. Final Answer:

   'Jane' 'Doe' -> Option C

4. Quick Check:

   Setter splits and assigns names = 'Jane' 'Doe' [OK]

Hint: Setter splits string and updates refs accordingly [OK]

Common Mistakes:

• Expecting full string in firstName
• Thinking computed properties are read-only
• Confusing ref.value and computed.value

4.

What is wrong with this computed property definition in Vue 3?

const fullName = computed({
  get: () => {
    return firstName.value + ' ' + lastName.value
  },
  set: (value) => {
    const names = value.split(' ')
    firstName.value = names[0]
    lastName.value = names[1]
  }
})

medium

A. Arrow functions break the reactivity context for get and set

B. Missing commas between get and set

C. Cannot use computed with set method

D. Must use async functions for get and set

Solution

1. Step 1: Analyze arrow function usage

   Arrow functions do not bind their own this, which can break reactivity when accessing reactive refs inside get/set.

2. Step 2: Understand Vue reactivity context

   Using normal function syntax ensures correct reactivity and access to reactive data.

3. Final Answer:

   Arrow functions break the reactivity context for get and set -> Option A

4. Quick Check:

   Use normal functions, not arrow, for computed get/set [OK]

Hint: Avoid arrow functions in computed get/set [OK]

Common Mistakes:

• Using arrow functions for get/set
• Thinking commas are missing
• Believing set is not allowed

5.

You want to create a computed property fullName that updates firstName and lastName refs, but also trims extra spaces and handles single names gracefully. Which computed property definition is best?

const fullName = computed({
  get() {
    return `${firstName.value.trim()} ${lastName.value.trim()}`.trim()
  },
  set(value) {
    const names = value.trim().split(/\s+/)
    firstName.value = names[0] || ''
    lastName.value = names.slice(1).join(' ') || ''
  }
})

hard

A. Setter should not use slice, only split

B. It will fail if value is empty string

C. Getter should not trim values

D. This handles trimming and single names correctly

Solution

1. Step 1: Check trimming in getter

   The getter trims both first and last names and then trims the combined string to avoid extra spaces.

2. Step 2: Analyze setter logic

   The setter trims input, splits by spaces, assigns first word to firstName, and joins the rest for lastName, handling single names gracefully.

3. Final Answer:

   This handles trimming and single names correctly -> Option D

4. Quick Check:

   Trim and split with fallback = robust computed set/get [OK]

Hint: Trim inputs and handle missing last name with slice [OK]

Common Mistakes:

• Not trimming input causing extra spaces
• Failing on single-word names
• Using split without regex for multiple spaces