Vue.js • Chapter 9 • Foundations to Advanced
Conditional Rendering
Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.
9.1 v-if
v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to v-if and trace how it changes the rendered interface. In Chapter 9, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For v-if in Chapter 9, 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 v-if to conditional rendering. 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
v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to v-if and trace how it changes the rendered interface.
10 teaching examples
Example 1: Smallest useful case
Build the smallest shopping cart that demonstrates v-if. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to v-if and trace how it changes the rendered interface. This is example 1 for Chapter 9, topic 1.
Example 2: Change one reactive value
Change one value involved in v-if 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 v-if 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 v-if edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use v-if in the admin table while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to v-if and trace how it changes the rendered interface. This is example 5 for Chapter 9, topic 1.
Example 6: State ownership review
Remove duplicated state from the photo gallery. For v-if, 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 v-if. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the v-if 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 v-if. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review v-if in the quiz screen for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to v-if and trace how it changes the rendered interface. This is example 10 for Chapter 9, topic 1.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "v-if"
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 v-if.
- 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 v-if and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on v-if from Chapter 9. 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.
9.2 v-else
v-else is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 9, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For v-else in Chapter 9, 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 v-else to conditional rendering. 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
v-else is a focused part of Vue application design in Chapter 9. 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 v-else. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. v-else is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 9, topic 2.
Example 2: Change one reactive value
Change one value involved in v-else 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 v-else 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 v-else edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use v-else in the task board while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. v-else is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 9, topic 2.
Example 6: State ownership review
Remove duplicated state from the language selector. For v-else, 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 v-else. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the v-else 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 v-else. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review v-else in the course dashboard for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. v-else is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 9, topic 2.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "v-else"
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 v-else.
- 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 v-else and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on v-else from Chapter 9. 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.
9.3 v-else-if
v-else-if is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 9, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For v-else-if in Chapter 9, 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 v-else-if to conditional rendering. 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
v-else-if is a focused part of Vue application design in Chapter 9. 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 v-else-if. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. v-else-if is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 9, topic 3.
Example 2: Change one reactive value
Change one value involved in v-else-if 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 v-else-if 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 v-else-if edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use v-else-if in the analytics view while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. v-else-if is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 9, topic 3.
Example 6: State ownership review
Remove duplicated state from the support form. For v-else-if, 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 v-else-if. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the v-else-if 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 v-else-if. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review v-else-if in the shopping cart for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. v-else-if is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 9, topic 3.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "v-else-if"
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 v-else-if.
- 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 v-else-if and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on v-else-if from Chapter 9. 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.
9.4 v-show
v-show is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 9, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For v-show in Chapter 9, 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 v-show to conditional rendering. 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
v-show is a focused part of Vue application design in Chapter 9. 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 v-show. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. v-show is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 9, topic 4.
Example 2: Change one reactive value
Change one value involved in v-show 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 v-show 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 v-show edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use v-show in the profile editor while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. v-show is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 9, topic 4.
Example 6: State ownership review
Remove duplicated state from the search panel. For v-show, 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 v-show. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the v-show 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 v-show. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review v-show in the message panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. v-show is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 9, topic 4.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "v-show"
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 v-show.
- 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 v-show and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on v-show from Chapter 9. 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.
9.5 Choosing v-if or v-show
v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to Choosing v-if or v-show and trace how it changes the rendered interface. In Chapter 9, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Choosing v-if or v-show in Chapter 9, 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 v-if or v-show to conditional rendering. 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
v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to Choosing v-if or v-show and trace how it changes the rendered interface.
10 teaching examples
Example 1: Smallest useful case
Build the smallest course dashboard that demonstrates Choosing v-if or v-show. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to Choosing v-if or v-show and trace how it changes the rendered interface. This is example 1 for Chapter 9, topic 5.
Example 2: Change one reactive value
Change one value involved in Choosing v-if or v-show 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 Choosing v-if or v-show 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 Choosing v-if or v-show edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Choosing v-if or v-show in the lesson tracker while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to Choosing v-if or v-show and trace how it changes the rendered interface. This is example 5 for Chapter 9, topic 5.
Example 6: State ownership review
Remove duplicated state from the booking form. For Choosing v-if or v-show, 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 Choosing v-if or v-show. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Choosing v-if or v-show 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 Choosing v-if or v-show. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Choosing v-if or v-show in the notification center for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to Choosing v-if or v-show and trace how it changes the rendered interface. This is example 10 for Chapter 9, topic 5.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Choosing v-if or v-show"
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 v-if or v-show.
- 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 v-if or v-show and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Choosing v-if or v-show from Chapter 9. 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 9 review — 10 questions and answers
1. What is the purpose of v-if?
Answer: v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to v-if and trace how it changes the rendered interface.
2. What should you inspect when v-if 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 v-else?
Answer: v-else is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
4. What should you inspect when v-else 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 v-else-if?
Answer: v-else-if is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
6. What should you inspect when v-else-if 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 v-show?
Answer: v-show is a focused part of Vue application design in Chapter 9. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
8. What should you inspect when v-show 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 v-if or v-show?
Answer: v-if conditionally creates or removes a rendered block according to a truthy or falsy expression. In Chapter 9, apply this definition specifically to Choosing v-if or v-show and trace how it changes the rendered interface.
10. What should you inspect when Choosing v-if or v-show 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.