Vue.js • Chapter 42 • Foundations to Advanced
Reusable Component API Design
Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.
42.1 Prop Design
Prop Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 42, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Prop Design in Chapter 42, inspect component ownership, data direction, event payloads, and the public component contract. 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 Prop Design to reusable component api design. 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
Prop Design is a focused part of Vue application design in Chapter 42. 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 Prop Design. Keep one input and one visible result, then explain component ownership, data direction, event payloads, and the public component contract. Prop Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 42, topic 1.
Example 2: Change one reactive value
Change one value involved in Prop Design 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 Prop Design 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 Prop Design edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Prop Design in the admin table while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Prop Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 42, topic 1.
Example 6: State ownership review
Remove duplicated state from the photo gallery. For Prop Design, 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 Prop Design. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Prop Design 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 Prop Design. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Prop Design in the quiz screen for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Prop Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 42, topic 1.
Vue code example
<script setup>
defineProps({ title: { type: String, required: true }, active: Boolean })
</script>
<template><article :class="{ active }"><h2>{{ title }}</h2></article></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Prop Design.
- 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 Prop Design and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Prop Design from Chapter 42. 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.
42.2 Event Design
Event Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 42, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Event Design in Chapter 42, inspect component ownership, data direction, event payloads, and the public component contract. 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 Event Design to reusable component api design. 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
Event Design is a focused part of Vue application design in Chapter 42. 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 Event Design. Keep one input and one visible result, then explain component ownership, data direction, event payloads, and the public component contract. Event Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 42, topic 2.
Example 2: Change one reactive value
Change one value involved in Event Design 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 Event Design 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 Event Design edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Event Design in the task board while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Event Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 42, topic 2.
Example 6: State ownership review
Remove duplicated state from the language selector. For Event Design, 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 Event Design. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Event Design 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 Event Design. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Event Design in the course dashboard for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Event Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 42, topic 2.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Event Design"
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 Event Design.
- 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 Event Design and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Event Design from Chapter 42. 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.
42.3 Slot Design
A slot lets a parent provide template content for a child component to render in a defined location. In Chapter 42, apply this definition specifically to Slot Design and trace how it changes the rendered interface. In Chapter 42, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Slot Design in Chapter 42, inspect component ownership, data direction, event payloads, and the public component contract. 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 Slot Design to reusable component api design. 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
A slot lets a parent provide template content for a child component to render in a defined location. In Chapter 42, apply this definition specifically to Slot Design and trace how it changes the rendered interface.
10 teaching examples
Example 1: Smallest useful case
Build the smallest notification center that demonstrates Slot Design. Keep one input and one visible result, then explain component ownership, data direction, event payloads, and the public component contract. A slot lets a parent provide template content for a child component to render in a defined location. In Chapter 42, apply this definition specifically to Slot Design and trace how it changes the rendered interface. This is example 1 for Chapter 42, topic 3.
Example 2: Change one reactive value
Change one value involved in Slot Design 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 Slot Design 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 Slot Design edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Slot Design in the analytics view while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A slot lets a parent provide template content for a child component to render in a defined location. In Chapter 42, apply this definition specifically to Slot Design and trace how it changes the rendered interface. This is example 5 for Chapter 42, topic 3.
Example 6: State ownership review
Remove duplicated state from the support form. For Slot Design, 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 Slot Design. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Slot Design 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 Slot Design. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Slot Design in the shopping cart for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A slot lets a parent provide template content for a child component to render in a defined location. In Chapter 42, apply this definition specifically to Slot Design and trace how it changes the rendered interface. This is example 10 for Chapter 42, topic 3.
Vue code example
<template><section><header><slot name="title">Default title</slot></header><main><slot /></main></section></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Slot Design.
- 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 Slot Design and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Slot Design from Chapter 42. 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.
42.4 Exposed Methods
Exposed Methods is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 42, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Exposed Methods in Chapter 42, 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 Exposed Methods to reusable component api design. 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
Exposed Methods is a focused part of Vue application design in Chapter 42. 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 Exposed Methods. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Exposed Methods is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 42, topic 4.
Example 2: Change one reactive value
Change one value involved in Exposed Methods 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 Exposed Methods 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 Exposed Methods edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Exposed Methods in the profile editor while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Exposed Methods is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 42, topic 4.
Example 6: State ownership review
Remove duplicated state from the search panel. For Exposed 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 shopping cart has a slow request while using Exposed Methods. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Exposed Methods 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 Exposed Methods. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Exposed Methods in the message panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Exposed Methods is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 42, topic 4.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Exposed Methods"
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 Exposed 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 Exposed Methods and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Exposed Methods from Chapter 42. 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.
42.5 Avoiding Over-Configuration
Avoiding Over-Configuration is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 42, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Avoiding Over-Configuration in Chapter 42, 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 Avoiding Over-Configuration to reusable component api design. 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
Avoiding Over-Configuration is a focused part of Vue application design in Chapter 42. 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 Avoiding Over-Configuration. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Avoiding Over-Configuration is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 42, topic 5.
Example 2: Change one reactive value
Change one value involved in Avoiding Over-Configuration 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 Avoiding Over-Configuration 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 Avoiding Over-Configuration edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Avoiding Over-Configuration in the lesson tracker while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Avoiding Over-Configuration is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 42, topic 5.
Example 6: State ownership review
Remove duplicated state from the booking form. For Avoiding Over-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 message panel has a slow request while using Avoiding Over-Configuration. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Avoiding Over-Configuration 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 Avoiding Over-Configuration. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Avoiding Over-Configuration in the notification center for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Avoiding Over-Configuration is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 42, topic 5.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Avoiding Over-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 Avoiding Over-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 Avoiding Over-Configuration and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Avoiding Over-Configuration from Chapter 42. 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 42 review — 10 questions and answers
1. What is the purpose of Prop Design?
Answer: Prop Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
2. What should you inspect when Prop Design behaves unexpectedly?
Answer: Inspect component ownership, data direction, event payloads, and the public component contract. Reduce the feature to a small component and trace reactive input through the rendered result.
3. What is the purpose of Event Design?
Answer: Event Design is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
4. What should you inspect when Event Design behaves unexpectedly?
Answer: Inspect component ownership, data direction, event payloads, and the public component contract. Reduce the feature to a small component and trace reactive input through the rendered result.
5. What is the purpose of Slot Design?
Answer: A slot lets a parent provide template content for a child component to render in a defined location. In Chapter 42, apply this definition specifically to Slot Design and trace how it changes the rendered interface.
6. What should you inspect when Slot Design behaves unexpectedly?
Answer: Inspect component ownership, data direction, event payloads, and the public component contract. Reduce the feature to a small component and trace reactive input through the rendered result.
7. What is the purpose of Exposed Methods?
Answer: Exposed Methods is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
8. What should you inspect when Exposed Methods 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 Avoiding Over-Configuration?
Answer: Avoiding Over-Configuration is a focused part of Vue application design in Chapter 42. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10. What should you inspect when Avoiding Over-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.