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