Vue.js • Chapter 27 • Foundations to Advanced
KeepAlive
Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.
27.1 Caching Component Instances
Caching Component Instances is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 27, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Caching Component Instances in Chapter 27, inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. 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 Caching Component Instances to keepalive. 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
Caching Component Instances is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10 teaching examples
Example 1: Smallest useful case
Build the smallest shopping cart that demonstrates Caching Component Instances. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Caching Component Instances is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 27, topic 1.
Example 2: Change one reactive value
Change one value involved in Caching Component Instances inside the lesson tracker. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Caching Component Instances across two components in the booking form. 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 message panel. Handle the Caching Component Instances edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Caching Component Instances in the admin table while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Caching Component Instances is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 27, topic 1.
Example 6: State ownership review
Remove duplicated state from the photo gallery. For Caching Component Instances, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the notification center has a slow request while using Caching Component Instances. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Caching Component Instances responsibility from a crowded task board into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the language selector before optimizing Caching Component Instances. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Caching Component Instances in the quiz screen for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Caching Component Instances is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 27, topic 1.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Caching Component Instances"
const active = ref(false)
</script>
<template>
<section><h2>{{ topic }}</h2><button :aria-pressed="active" @click="active=!active">Toggle state</button><p>{{ active ? 'Active' : 'Inactive' }}</p></section>
</template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Caching Component Instances.
- 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 Caching Component Instances and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Caching Component Instances from Chapter 27. 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.
27.2 include and exclude
include and exclude is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 27, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For include and exclude in Chapter 27, inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. 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 include and exclude to keepalive. 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
include and exclude is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10 teaching examples
Example 1: Smallest useful case
Build the smallest message panel that demonstrates include and exclude. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. include and exclude is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 27, topic 2.
Example 2: Change one reactive value
Change one value involved in include and exclude inside the admin table. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use include and exclude across two components in the photo gallery. 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 notification center. Handle the include and exclude edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use include and exclude in the task board while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. include and exclude is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 27, topic 2.
Example 6: State ownership review
Remove duplicated state from the language selector. For include and exclude, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the quiz screen has a slow request while using include and exclude. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the include and exclude responsibility from a crowded analytics view into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the support form before optimizing include and exclude. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review include and exclude in the course dashboard for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. include and exclude is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 27, topic 2.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "include and exclude"
const active = ref(false)
</script>
<template>
<section><h2>{{ topic }}</h2><button :aria-pressed="active" @click="active=!active">Toggle state</button><p>{{ active ? 'Active' : 'Inactive' }}</p></section>
</template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by include and exclude.
- 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 include and exclude and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on include and exclude from Chapter 27. 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.
27.3 max
max is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 27, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For max in Chapter 27, inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. 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 max to keepalive. 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
max is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10 teaching examples
Example 1: Smallest useful case
Build the smallest notification center that demonstrates max. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. max is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 27, topic 3.
Example 2: Change one reactive value
Change one value involved in max inside the task board. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use max across two components in the language selector. 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 quiz screen. Handle the max edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use max in the analytics view while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. max is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 27, topic 3.
Example 6: State ownership review
Remove duplicated state from the support form. For max, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the course dashboard has a slow request while using max. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the max responsibility from a crowded profile editor into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the search panel before optimizing max. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review max in the shopping cart for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. max is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 27, topic 3.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "max"
const active = ref(false)
</script>
<template>
<section><h2>{{ topic }}</h2><button :aria-pressed="active" @click="active=!active">Toggle state</button><p>{{ active ? 'Active' : 'Inactive' }}</p></section>
</template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by max.
- 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 max and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on max from Chapter 27. 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.
27.4 Activated and Deactivated Hooks
Activated and Deactivated Hooks is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 27, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Activated and Deactivated Hooks in Chapter 27, inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. 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 Activated and Deactivated Hooks to keepalive. 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
Activated and Deactivated Hooks is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10 teaching examples
Example 1: Smallest useful case
Build the smallest quiz screen that demonstrates Activated and Deactivated Hooks. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Activated and Deactivated Hooks is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 27, topic 4.
Example 2: Change one reactive value
Change one value involved in Activated and Deactivated Hooks inside the analytics view. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Activated and Deactivated Hooks across two components in the support form. 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 course dashboard. Handle the Activated and Deactivated Hooks edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Activated and Deactivated Hooks in the profile editor while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Activated and Deactivated Hooks is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 27, topic 4.
Example 6: State ownership review
Remove duplicated state from the search panel. For Activated and Deactivated Hooks, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the shopping cart has a slow request while using Activated and Deactivated Hooks. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Activated and Deactivated Hooks responsibility from a crowded lesson tracker into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the booking form before optimizing Activated and Deactivated Hooks. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Activated and Deactivated Hooks in the message panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Activated and Deactivated Hooks is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 27, topic 4.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Activated and Deactivated Hooks"
const active = ref(false)
</script>
<template>
<section><h2>{{ topic }}</h2><button :aria-pressed="active" @click="active=!active">Toggle state</button><p>{{ active ? 'Active' : 'Inactive' }}</p></section>
</template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Activated and Deactivated Hooks.
- 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 Activated and Deactivated Hooks and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Activated and Deactivated Hooks from Chapter 27. 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.
27.5 State Preservation
State Preservation is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 27, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For State Preservation in Chapter 27, inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. 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 State Preservation to keepalive. 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
State Preservation is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10 teaching examples
Example 1: Smallest useful case
Build the smallest course dashboard that demonstrates State Preservation. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. State Preservation is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 27, topic 5.
Example 2: Change one reactive value
Change one value involved in State Preservation inside the profile editor. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use State Preservation across two components in the search panel. 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 shopping cart. Handle the State Preservation edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use State Preservation in the lesson tracker while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. State Preservation is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 27, topic 5.
Example 6: State ownership review
Remove duplicated state from the booking form. For State Preservation, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the message panel has a slow request while using State Preservation. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the State Preservation responsibility from a crowded admin table into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the photo gallery before optimizing State Preservation. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review State Preservation in the notification center for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. State Preservation is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 27, topic 5.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "State Preservation"
const active = ref(false)
</script>
<template>
<section><h2>{{ topic }}</h2><button :aria-pressed="active" @click="active=!active">Toggle state</button><p>{{ active ? 'Active' : 'Inactive' }}</p></section>
</template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by State Preservation.
- 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 State Preservation and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on State Preservation from Chapter 27. 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 27 review — 10 questions and answers
1. What is the purpose of Caching Component Instances?
Answer: Caching Component Instances is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
2. What should you inspect when Caching Component Instances behaves unexpectedly?
Answer: Inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Reduce the feature to a small component and trace reactive input through the rendered result.
3. What is the purpose of include and exclude?
Answer: include and exclude is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
4. What should you inspect when include and exclude behaves unexpectedly?
Answer: Inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Reduce the feature to a small component and trace reactive input through the rendered result.
5. What is the purpose of max?
Answer: max is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
6. What should you inspect when max behaves unexpectedly?
Answer: Inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Reduce the feature to a small component and trace reactive input through the rendered result.
7. What is the purpose of Activated and Deactivated Hooks?
Answer: Activated and Deactivated Hooks is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
8. What should you inspect when Activated and Deactivated Hooks behaves unexpectedly?
Answer: Inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Reduce the feature to a small component and trace reactive input through the rendered result.
9. What is the purpose of State Preservation?
Answer: State Preservation is a focused part of Vue application design in Chapter 27. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10. What should you inspect when State Preservation behaves unexpectedly?
Answer: Inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Reduce the feature to a small component and trace reactive input through the rendered result.