Vue.js • Chapter 6 • Foundations to Advanced

Reactivity Fundamentals

Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.

5 topics50 teaching examplesCode example per topic10 Q&A

Estimated reading time0% read

6.1 What Reactivity Means

What Reactivity Means is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 6, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For What Reactivity Means in Chapter 6, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. 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 What Reactivity Means to reactivity fundamentals. 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

What Reactivity Means is a focused part of Vue application design in Chapter 6. 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 What Reactivity Means. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. What Reactivity Means is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 6, topic 1.
Example 2: Change one reactive value
Change one value involved in What Reactivity Means 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 What Reactivity Means 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 What Reactivity Means edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use What Reactivity Means in the admin table while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. What Reactivity Means is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 6, topic 1.
Example 6: State ownership review
Remove duplicated state from the photo gallery. For What Reactivity Means, 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 What Reactivity Means. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the What Reactivity Means 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 What Reactivity Means. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review What Reactivity Means in the quiz screen for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. What Reactivity Means is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 6, topic 1.

Vue code example

<script setup>
import { ref } from 'vue'
const topic = "What Reactivity Means"
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 What Reactivity Means.
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 What Reactivity Means and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on What Reactivity Means from Chapter 6. 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.

6.2 ref

A ref stores a reactive value; JavaScript uses .value while templates usually unwrap it automatically. In Chapter 6, apply this definition specifically to ref and trace how it changes the rendered interface. In Chapter 6, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For ref in Chapter 6, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. 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 ref to reactivity fundamentals. 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

10 teaching examples

Example 1: Smallest useful case
Build the smallest message panel that demonstrates ref. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A ref stores a reactive value; JavaScript uses .value while templates usually unwrap it automatically. In Chapter 6, apply this definition specifically to ref and trace how it changes the rendered interface. This is example 1 for Chapter 6, topic 2.
Example 2: Change one reactive value
Change one value involved in ref 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 ref 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 ref edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use ref in the task board while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A ref stores a reactive value; JavaScript uses .value while templates usually unwrap it automatically. In Chapter 6, apply this definition specifically to ref and trace how it changes the rendered interface. This is example 5 for Chapter 6, topic 2.
Example 6: State ownership review
Remove duplicated state from the language selector. For ref, 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 ref. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the ref 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 ref. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review ref in the course dashboard for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A ref stores a reactive value; JavaScript uses .value while templates usually unwrap it automatically. In Chapter 6, apply this definition specifically to ref and trace how it changes the rendered interface. This is example 10 for Chapter 6, topic 2.

Vue code example

<script setup>
import { ref } from 'vue'
const topic = "ref"
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 ref.
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 ref and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on ref from Chapter 6. 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.

6.3 reactive

reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to reactive and trace how it changes the rendered interface. In Chapter 6, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For reactive in Chapter 6, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. 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 reactive to reactivity fundamentals. 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

10 teaching examples

Example 1: Smallest useful case
Build the smallest notification center that demonstrates reactive. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to reactive and trace how it changes the rendered interface. This is example 1 for Chapter 6, topic 3.
Example 2: Change one reactive value
Change one value involved in reactive 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 reactive 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 reactive edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use reactive in the analytics view while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to reactive and trace how it changes the rendered interface. This is example 5 for Chapter 6, topic 3.
Example 6: State ownership review
Remove duplicated state from the support form. For reactive, 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 reactive. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the reactive 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 reactive. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review reactive in the shopping cart for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to reactive and trace how it changes the rendered interface. This is example 10 for Chapter 6, topic 3.

Vue code example

<script setup>
import { ref } from 'vue'
const topic = "reactive"
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 reactive.
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 reactive and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on reactive from Chapter 6. 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.

6.4 Reading and Updating Reactive Values

reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to Reading and Updating Reactive Values and trace how it changes the rendered interface. In Chapter 6, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Reading and Updating Reactive Values in Chapter 6, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. 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 Reading and Updating Reactive Values to reactivity fundamentals. 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

10 teaching examples

Example 1: Smallest useful case
Build the smallest quiz screen that demonstrates Reading and Updating Reactive Values. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to Reading and Updating Reactive Values and trace how it changes the rendered interface. This is example 1 for Chapter 6, topic 4.
Example 2: Change one reactive value
Change one value involved in Reading and Updating Reactive Values 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 Reading and Updating Reactive Values 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 Reading and Updating Reactive Values edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Reading and Updating Reactive Values in the profile editor while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to Reading and Updating Reactive Values and trace how it changes the rendered interface. This is example 5 for Chapter 6, topic 4.
Example 6: State ownership review
Remove duplicated state from the search panel. For Reading and Updating Reactive Values, 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 Reading and Updating Reactive Values. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Reading and Updating Reactive Values 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 Reading and Updating Reactive Values. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Reading and Updating Reactive Values in the message panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. reactive creates a proxy around an object so Vue can track reads and writes that affect rendering. In Chapter 6, apply this definition specifically to Reading and Updating Reactive Values and trace how it changes the rendered interface. This is example 10 for Chapter 6, topic 4.

Vue code example

<script setup>
import { ref } from 'vue'
const topic = "Reading and Updating Reactive Values"
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 Reading and Updating Reactive Values.
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 Reading and Updating Reactive Values and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Reading and Updating Reactive Values from Chapter 6. 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.

6.5 Deep and Shallow Reactivity

Deep and Shallow Reactivity is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 6, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.

For Deep and Shallow Reactivity in Chapter 6, inspect reactive dependencies, update timing, derived values, side effects, and cleanup. 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 Deep and Shallow Reactivity to reactivity fundamentals. 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

10 teaching examples

Example 1: Smallest useful case
Build the smallest course dashboard that demonstrates Deep and Shallow Reactivity. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. Deep and Shallow Reactivity is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 6, topic 5.
Example 2: Change one reactive value
Change one value involved in Deep and Shallow Reactivity 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 Deep and Shallow Reactivity 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 Deep and Shallow Reactivity edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Deep and Shallow Reactivity in the lesson tracker while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Deep and Shallow Reactivity is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 6, topic 5.
Example 6: State ownership review
Remove duplicated state from the booking form. For Deep and Shallow Reactivity, 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 Deep and Shallow Reactivity. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Deep and Shallow Reactivity 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 Deep and Shallow Reactivity. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Deep and Shallow Reactivity in the notification center for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Deep and Shallow Reactivity is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 6, topic 5.

Vue code example

<script setup>
import { ref } from 'vue'
const topic = "Deep and Shallow Reactivity"
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 Deep and Shallow Reactivity.
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 Deep and Shallow Reactivity and updates according to the interaction or data in the example.

Practice exercise

Create a small Vue feature focused on Deep and Shallow Reactivity from Chapter 6. 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 6 review — 10 questions and answers

1. What is the purpose of What Reactivity Means?

Answer: What Reactivity Means is a focused part of Vue application design in Chapter 6. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.

2. What should you inspect when What Reactivity Means behaves unexpectedly?