v-once for static content in Vue - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does v-once do in this Vue component?

Consider this Vue template snippet:

<template>
  <div>
    <h1 v-once>Hello, {{ name }}!</h1>
    <button @click="changeName">Change Name</button>
  </div>
</template>

<script setup>
import { ref } from 'vue'
const name = ref('Alice')
function changeName() {
  name.value = 'Bob'
}
</script>

What will be displayed inside the <h1> after clicking the button?

Vue

<template>
  <div>
    <h1 v-once>Hello, {{ name }}!</h1>
    <button @click="changeName">Change Name</button>
  </div>
</template>

<script setup>
import { ref } from 'vue'
const name = ref('Alice')
function changeName() {
  name.value = 'Bob'
}
</script>

A It stays 'Hello, Alice!' even after clicking the button.

B It causes a runtime error because v-once cannot be used with variables.

C It shows 'Hello, Bob!' only after refreshing the page.

D It updates to 'Hello, Bob!' immediately after clicking the button.

💡 Hint

Think about what v-once does to the element's rendering and updates.

The v-once directive tells Vue to render the element only once and skip future updates. So, even if the name changes, the content inside the <h1> does not update and stays as initially rendered.

❓ state_output

intermediate

How many times is the computedValue updated with v-once?

Given this Vue component:

<template>
  <p v-once>Computed: {{ computedValue }}</p>
  <button @click="increment">Increment</button>
</template>

<script setup>
import { ref, computed } from 'vue'
const count = ref(0)
const computedValue = computed(() => count.value * 2)
function increment() {
  count.value++
}
</script>

How many times will the computedValue be updated and reflected in the UI after clicking the button 3 times?

Vue

<template>
  <p v-once>Computed: {{ computedValue }}</p>
  <button @click="increment">Increment</button>
</template>

<script setup>
import { ref, computed } from 'vue'
const count = ref(0)
const computedValue = computed(() => count.value * 2)
function increment() {
  count.value++
}
</script>

A The computed value updates but the UI does not reflect changes until refresh.

B The computed value updates and shows 2, 4, 6 after each click.

C The computed value causes an error because v-once blocks computed properties.

D The computed value is shown only once with initial value 0 and never updates.

💡 Hint

Remember what v-once does to the element's reactivity.

The v-once directive renders the element only once and disables future updates. So, even though computedValue changes, the UI inside the <p> does not update after the first render.

📝 Syntax

advanced

Which option correctly uses v-once to optimize static content?

You want to render a static list of items that never change. Which Vue template snippet correctly uses v-once to optimize rendering?

A

<ul>
  <li v-for="item in items" :key="item.id" v-once>{{ item.name }}</li>
</ul>

B

<ul v-once>
  <li v-for="item in items" :key="item.id">{{ item.name }}</li>
</ul>

C

<ul>
  <li v-for="item in items" :key="item.id">{{ item.name }}</li>
</ul> <!-- v-once on comment -->

D

<ul v-once>
  <li v-for="item in items">{{ item.name }}</li>
</ul>

💡 Hint

Think about how v-once works with v-for and keys.

Applying v-once on each <li> inside the v-for loop ensures each list item is rendered once and not updated later. Option A correctly places v-once on the <li> with a :key. Option A applies v-once on the whole <ul>, but the list is dynamic and Vue expects keys on children for updates. Option A misses keys, which is required for v-for. Option A is invalid as v-once on a comment does nothing.

🔧 Debug

advanced

Why does this Vue component not update the static text inside v-once after state change?

Look at this Vue component:

<template>
  <div>
    <p v-once>Static message: {{ message }}</p>
    <button @click="updateMessage">Update</button>
  </div>
</template>

<script setup>
import { ref } from 'vue'
const message = ref('Hello')
function updateMessage() {
  message.value = 'Goodbye'
}
</script>

Why does the text inside <p> not change after clicking the button?

Vue

<template>
  <div>
    <p v-once>Static message: {{ message }}</p>
    <button @click="updateMessage">Update</button>
  </div>
</template>

<script setup>
import { ref } from 'vue'
const message = ref('Hello')
function updateMessage() {
  message.value = 'Goodbye'
}
</script>

A Because the message variable is not reactive and does not trigger updates.

B Because v-once renders the element only once and disables future updates.

C Because the button click handler is not correctly bound to the updateMessage function.

D Because Vue requires a key attribute on the <p> element to update it.

💡 Hint

Think about what v-once does to the element's rendering lifecycle.

The v-once directive tells Vue to render the element only once and skip all future updates. So, even though message changes, the content inside the <p> does not update.

🧠 Conceptual

expert

What is the main benefit of using v-once in Vue components?

Choose the best explanation for why and when to use v-once in Vue templates.

A It enables two-way data binding for static content to keep it reactive.

B It automatically caches API responses to reduce network requests.

C It improves performance by rendering static content only once and skipping future updates.

D It forces Vue to re-render the element every time the state changes.

💡 Hint

Think about what happens when you have content that never changes.

v-once is used to optimize performance by telling Vue to render an element only once and skip all future updates. This is useful for static content that does not change during the component's lifecycle.