Vue.js • Chapter 7 • Foundations to Advanced

Computed Properties

Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.

5 topics50 teaching examplesCode example per topic10 Q&A

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7.1 Creating Computed Values

A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Creating Computed Values and trace how it changes the rendered interface. In Chapter 7, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Creating Computed Values in Chapter 7, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Keep writable state ownership explicit, derive values when possible, and separate display calculations from network, DOM, storage, timer, or other external work.

This lesson connects Creating Computed Values to computed properties. Start with one working case, verify the expected output, then add one edge case and explain what Vue tracks, reuses, creates, removes, or updates.

Concept in plain language

10 teaching examples

Example 1: Smallest useful case
Build the smallest photo gallery that demonstrates Creating Computed Values. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Creating Computed Values and trace how it changes the rendered interface. This is example 1 for Chapter 7, topic 1.
Example 2: Change one reactive value
Change one value involved in Creating Computed Values inside the notification center. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Creating Computed Values across two components in the task board. Compare which component owns the writable data and which component only receives or presents it.
Example 4: Edge case
Add an empty, missing, invalid, delayed, or rapidly changing value to the language selector. Handle the Creating Computed Values edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Creating Computed Values in the quiz screen while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Creating Computed Values and trace how it changes the rendered interface. This is example 5 for Chapter 7, topic 1.
Example 6: State ownership review
Remove duplicated state from the analytics view. For Creating Computed Values, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the support form has a slow request while using Creating Computed Values. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Creating Computed Values responsibility from a crowded course dashboard into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the profile editor before optimizing Creating Computed Values. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Creating Computed Values in the search panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Creating Computed Values and trace how it changes the rendered interface. This is example 10 for Chapter 7, topic 1.

Vue code example

<script setup>
import { ref, computed } from 'vue'
const price = ref(20)
const quantity = ref(2)
const total = computed(() => price.value * quantity.value)
</script>
<template><p>Total: {{ total }}</p><button @click="quantity++">Add one</button></template>

Step-by-step code explanation

Identify the Vue responsibility demonstrated by Creating Computed Values.
Read the reactive state, props, route/store input, or injected value before the template.
Trace the event, dependency, watcher, lifecycle hook, or navigation action that changes the display.
Test one normal path and one edge case, including cleanup when external work is involved.
Confirm accessibility, mobile width, and RTL behavior for user-facing controls and translated text.

Expected behavior: A small Vue interface demonstrates Creating Computed Values and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Creating Computed Values from Chapter 7. Predict the result before running it, test one edge case, and explain which reactive value, prop, event, route, store, or lifecycle step caused the update. Then check accessibility, narrow-screen width, and RTL behavior where relevant.

7.2 Computed Caching

A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Caching and trace how it changes the rendered interface. In Chapter 7, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Computed Caching in Chapter 7, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Keep writable state ownership explicit, derive values when possible, and separate display calculations from network, DOM, storage, timer, or other external work.

This lesson connects Computed Caching to computed properties. Start with one working case, verify the expected output, then add one edge case and explain what Vue tracks, reuses, creates, removes, or updates.

Concept in plain language

10 teaching examples

Example 1: Smallest useful case
Build the smallest language selector that demonstrates Computed Caching. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Caching and trace how it changes the rendered interface. This is example 1 for Chapter 7, topic 2.
Example 2: Change one reactive value
Change one value involved in Computed Caching inside the quiz screen. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Computed Caching across two components in the analytics view. Compare which component owns the writable data and which component only receives or presents it.
Example 4: Edge case
Add an empty, missing, invalid, delayed, or rapidly changing value to the support form. Handle the Computed Caching edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Computed Caching in the course dashboard while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Caching and trace how it changes the rendered interface. This is example 5 for Chapter 7, topic 2.
Example 6: State ownership review
Remove duplicated state from the profile editor. For Computed Caching, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the search panel has a slow request while using Computed Caching. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Computed Caching responsibility from a crowded shopping cart into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the lesson tracker before optimizing Computed Caching. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Computed Caching in the booking form for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Caching and trace how it changes the rendered interface. This is example 10 for Chapter 7, topic 2.

Vue code example

<script setup>
import { ref, computed } from 'vue'
const price = ref(20)
const quantity = ref(2)
const total = computed(() => price.value * quantity.value)
</script>
<template><p>Total: {{ total }}</p><button @click="quantity++">Add one</button></template>

Step-by-step code explanation

Identify the Vue responsibility demonstrated by Computed Caching.
Read the reactive state, props, route/store input, or injected value before the template.
Trace the event, dependency, watcher, lifecycle hook, or navigation action that changes the display.
Test one normal path and one edge case, including cleanup when external work is involved.
Confirm accessibility, mobile width, and RTL behavior for user-facing controls and translated text.

Expected behavior: A small Vue interface demonstrates Computed Caching and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Computed Caching from Chapter 7. Predict the result before running it, test one edge case, and explain which reactive value, prop, event, route, store, or lifecycle step caused the update. Then check accessibility, narrow-screen width, and RTL behavior where relevant.

7.3 Writable Computed

A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Writable Computed and trace how it changes the rendered interface. In Chapter 7, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Writable Computed in Chapter 7, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Keep writable state ownership explicit, derive values when possible, and separate display calculations from network, DOM, storage, timer, or other external work.

This lesson connects Writable Computed to computed properties. Start with one working case, verify the expected output, then add one edge case and explain what Vue tracks, reuses, creates, removes, or updates.

Concept in plain language

10 teaching examples

Example 1: Smallest useful case
Build the smallest support form that demonstrates Writable Computed. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Writable Computed and trace how it changes the rendered interface. This is example 1 for Chapter 7, topic 3.
Example 2: Change one reactive value
Change one value involved in Writable Computed inside the course dashboard. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Writable Computed across two components in the profile editor. Compare which component owns the writable data and which component only receives or presents it.
Example 4: Edge case
Add an empty, missing, invalid, delayed, or rapidly changing value to the search panel. Handle the Writable Computed edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Writable Computed in the shopping cart while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Writable Computed and trace how it changes the rendered interface. This is example 5 for Chapter 7, topic 3.
Example 6: State ownership review
Remove duplicated state from the lesson tracker. For Writable Computed, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the booking form has a slow request while using Writable Computed. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Writable Computed responsibility from a crowded message panel into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the admin table before optimizing Writable Computed. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Writable Computed in the photo gallery for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Writable Computed and trace how it changes the rendered interface. This is example 10 for Chapter 7, topic 3.

Vue code example

<script setup>
import { ref, computed } from 'vue'
const price = ref(20)
const quantity = ref(2)
const total = computed(() => price.value * quantity.value)
</script>
<template><p>Total: {{ total }}</p><button @click="quantity++">Add one</button></template>

Step-by-step code explanation

Identify the Vue responsibility demonstrated by Writable Computed.
Read the reactive state, props, route/store input, or injected value before the template.
Trace the event, dependency, watcher, lifecycle hook, or navigation action that changes the display.
Test one normal path and one edge case, including cleanup when external work is involved.
Confirm accessibility, mobile width, and RTL behavior for user-facing controls and translated text.

Expected behavior: A small Vue interface demonstrates Writable Computed and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Writable Computed from Chapter 7. Predict the result before running it, test one edge case, and explain which reactive value, prop, event, route, store, or lifecycle step caused the update. Then check accessibility, narrow-screen width, and RTL behavior where relevant.

7.4 Computed vs Methods

A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed vs Methods and trace how it changes the rendered interface. In Chapter 7, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Computed vs Methods in Chapter 7, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Keep writable state ownership explicit, derive values when possible, and separate display calculations from network, DOM, storage, timer, or other external work.

This lesson connects Computed vs Methods to computed properties. Start with one working case, verify the expected output, then add one edge case and explain what Vue tracks, reuses, creates, removes, or updates.

Concept in plain language

10 teaching examples

Example 1: Smallest useful case
Build the smallest search panel that demonstrates Computed vs Methods. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed vs Methods and trace how it changes the rendered interface. This is example 1 for Chapter 7, topic 4.
Example 2: Change one reactive value
Change one value involved in Computed vs Methods inside the shopping cart. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Computed vs Methods across two components in the lesson tracker. Compare which component owns the writable data and which component only receives or presents it.
Example 4: Edge case
Add an empty, missing, invalid, delayed, or rapidly changing value to the booking form. Handle the Computed vs Methods edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Computed vs Methods in the message panel while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed vs Methods and trace how it changes the rendered interface. This is example 5 for Chapter 7, topic 4.
Example 6: State ownership review
Remove duplicated state from the admin table. For Computed vs Methods, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the photo gallery has a slow request while using Computed vs Methods. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Computed vs Methods responsibility from a crowded notification center into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the task board before optimizing Computed vs Methods. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Computed vs Methods in the language selector for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed vs Methods and trace how it changes the rendered interface. This is example 10 for Chapter 7, topic 4.

Vue code example

<script setup>
import { ref, computed } from 'vue'
const price = ref(20)
const quantity = ref(2)
const total = computed(() => price.value * quantity.value)
</script>
<template><p>Total: {{ total }}</p><button @click="quantity++">Add one</button></template>

Step-by-step code explanation

Identify the Vue responsibility demonstrated by Computed vs Methods.
Read the reactive state, props, route/store input, or injected value before the template.
Trace the event, dependency, watcher, lifecycle hook, or navigation action that changes the display.
Test one normal path and one edge case, including cleanup when external work is involved.
Confirm accessibility, mobile width, and RTL behavior for user-facing controls and translated text.

Expected behavior: A small Vue interface demonstrates Computed vs Methods and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Computed vs Methods from Chapter 7. Predict the result before running it, test one edge case, and explain which reactive value, prop, event, route, store, or lifecycle step caused the update. Then check accessibility, narrow-screen width, and RTL behavior where relevant.

7.5 Computed Dependencies

A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Dependencies and trace how it changes the rendered interface. In Chapter 7, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Computed Dependencies in Chapter 7, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Keep writable state ownership explicit, derive values when possible, and separate display calculations from network, DOM, storage, timer, or other external work.

This lesson connects Computed Dependencies to computed properties. Start with one working case, verify the expected output, then add one edge case and explain what Vue tracks, reuses, creates, removes, or updates.

Concept in plain language

10 teaching examples

Example 1: Smallest useful case
Build the smallest booking form that demonstrates Computed Dependencies. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Dependencies and trace how it changes the rendered interface. This is example 1 for Chapter 7, topic 5.
Example 2: Change one reactive value
Change one value involved in Computed Dependencies inside the message panel. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Computed Dependencies across two components in the admin table. Compare which component owns the writable data and which component only receives or presents it.
Example 4: Edge case
Add an empty, missing, invalid, delayed, or rapidly changing value to the photo gallery. Handle the Computed Dependencies edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Computed Dependencies in the notification center while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Dependencies and trace how it changes the rendered interface. This is example 5 for Chapter 7, topic 5.
Example 6: State ownership review
Remove duplicated state from the task board. For Computed Dependencies, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the language selector has a slow request while using Computed Dependencies. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Computed Dependencies responsibility from a crowded quiz screen into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the analytics view before optimizing Computed Dependencies. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Computed Dependencies in the support form for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Computed Dependencies and trace how it changes the rendered interface. This is example 10 for Chapter 7, topic 5.

Vue code example

<script setup>
import { ref, computed } from 'vue'
const price = ref(20)
const quantity = ref(2)
const total = computed(() => price.value * quantity.value)
</script>
<template><p>Total: {{ total }}</p><button @click="quantity++">Add one</button></template>

Step-by-step code explanation

Identify the Vue responsibility demonstrated by Computed Dependencies.
Read the reactive state, props, route/store input, or injected value before the template.
Trace the event, dependency, watcher, lifecycle hook, or navigation action that changes the display.
Test one normal path and one edge case, including cleanup when external work is involved.
Confirm accessibility, mobile width, and RTL behavior for user-facing controls and translated text.

Expected behavior: A small Vue interface demonstrates Computed Dependencies and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Computed Dependencies from Chapter 7. Predict the result before running it, test one edge case, and explain which reactive value, prop, event, route, store, or lifecycle step caused the update. Then check accessibility, narrow-screen width, and RTL behavior where relevant.

Chapter 7 review — 10 questions and answers

1. What is the purpose of Creating Computed Values?

Answer: A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 7, apply this definition specifically to Creating Computed Values and trace how it changes the rendered interface.

2. What should you inspect when Creating Computed Values behaves unexpectedly?