Vue.js • Chapter 13 • Foundations to Advanced
Lifecycle Hooks
Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.
13.1 onMounted
onMounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 13, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For onMounted in Chapter 13, 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 onMounted to lifecycle hooks. 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
onMounted is a focused part of Vue application design in Chapter 13. 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 photo gallery that demonstrates onMounted. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. onMounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 13, topic 1.
Example 2: Change one reactive value
Change one value involved in onMounted 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 onMounted 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 onMounted edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use onMounted in the quiz screen while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. onMounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 13, topic 1.
Example 6: State ownership review
Remove duplicated state from the analytics view. For onMounted, 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 onMounted. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the onMounted 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 onMounted. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review onMounted in the search panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. onMounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 13, topic 1.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "onMounted"
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 onMounted.
- 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 onMounted and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on onMounted from Chapter 13. 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.
13.2 onUpdated
onUpdated is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 13, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For onUpdated in Chapter 13, 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 onUpdated to lifecycle hooks. 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
onUpdated is a focused part of Vue application design in Chapter 13. 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 language selector that demonstrates onUpdated. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. onUpdated is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 13, topic 2.
Example 2: Change one reactive value
Change one value involved in onUpdated 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 onUpdated 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 onUpdated edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use onUpdated in the course dashboard while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. onUpdated is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 13, topic 2.
Example 6: State ownership review
Remove duplicated state from the profile editor. For onUpdated, 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 onUpdated. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the onUpdated 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 onUpdated. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review onUpdated in the booking form for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. onUpdated is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 13, topic 2.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "onUpdated"
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 onUpdated.
- 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 onUpdated and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on onUpdated from Chapter 13. 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.
13.3 onUnmounted
onUnmounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 13, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For onUnmounted in Chapter 13, 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 onUnmounted to lifecycle hooks. 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
onUnmounted is a focused part of Vue application design in Chapter 13. 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 support form that demonstrates onUnmounted. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. onUnmounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 13, topic 3.
Example 2: Change one reactive value
Change one value involved in onUnmounted 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 onUnmounted 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 onUnmounted edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use onUnmounted in the shopping cart while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. onUnmounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 13, topic 3.
Example 6: State ownership review
Remove duplicated state from the lesson tracker. For onUnmounted, 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 onUnmounted. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the onUnmounted 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 onUnmounted. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review onUnmounted in the photo gallery for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. onUnmounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 13, topic 3.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "onUnmounted"
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 onUnmounted.
- 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 onUnmounted and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on onUnmounted from Chapter 13. 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.
13.4 Lifecycle Timing
Lifecycle Timing is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 13, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Lifecycle Timing in Chapter 13, 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 Lifecycle Timing to lifecycle hooks. 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
Lifecycle Timing is a focused part of Vue application design in Chapter 13. 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 search panel that demonstrates Lifecycle Timing. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Lifecycle Timing is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 13, topic 4.
Example 2: Change one reactive value
Change one value involved in Lifecycle Timing 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 Lifecycle Timing 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 Lifecycle Timing edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Lifecycle Timing in the message panel while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Lifecycle Timing is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 13, topic 4.
Example 6: State ownership review
Remove duplicated state from the admin table. For Lifecycle Timing, 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 Lifecycle Timing. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Lifecycle Timing 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 Lifecycle Timing. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Lifecycle Timing in the language selector for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Lifecycle Timing is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 13, topic 4.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Lifecycle Timing"
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 Lifecycle Timing.
- 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 Lifecycle Timing and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Lifecycle Timing from Chapter 13. 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.
13.5 Choosing the Correct Hook
Choosing the Correct Hook is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 13, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Choosing the Correct Hook in Chapter 13, 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 Choosing the Correct Hook to lifecycle hooks. 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
Choosing the Correct Hook is a focused part of Vue application design in Chapter 13. 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 booking form that demonstrates Choosing the Correct Hook. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Choosing the Correct Hook is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 13, topic 5.
Example 2: Change one reactive value
Change one value involved in Choosing the Correct Hook 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 Choosing the Correct Hook 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 Choosing the Correct Hook edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Choosing the Correct Hook in the notification center while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Choosing the Correct Hook is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 13, topic 5.
Example 6: State ownership review
Remove duplicated state from the task board. For Choosing the Correct Hook, 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 Choosing the Correct Hook. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Choosing the Correct Hook 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 Choosing the Correct Hook. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Choosing the Correct Hook in the support form for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Choosing the Correct Hook is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 13, topic 5.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Choosing the Correct Hook"
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 Choosing the Correct Hook.
- 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 Choosing the Correct Hook and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Choosing the Correct Hook from Chapter 13. 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 13 review — 10 questions and answers
1. What is the purpose of onMounted?
Answer: onMounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
2. What should you inspect when onMounted 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 onUpdated?
Answer: onUpdated is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
4. What should you inspect when onUpdated 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 onUnmounted?
Answer: onUnmounted is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
6. What should you inspect when onUnmounted 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 Lifecycle Timing?
Answer: Lifecycle Timing is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
8. What should you inspect when Lifecycle Timing 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 Choosing the Correct Hook?
Answer: Choosing the Correct Hook is a focused part of Vue application design in Chapter 13. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10. What should you inspect when Choosing the Correct Hook 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.