Vue.js • Chapter 24 • Foundations to Advanced
Options API
Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.
24.1 data
data is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 24, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For data in Chapter 24, 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 data to options api. 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
data is a focused part of Vue application design in Chapter 24. 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 data. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. data is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 24, topic 1.
Example 2: Change one reactive value
Change one value involved in data 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 data 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 data edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use data in the admin table while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. data is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 24, topic 1.
Example 6: State ownership review
Remove duplicated state from the photo gallery. For data, 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 data. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the data 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 data. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review data in the quiz screen for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. data is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 24, topic 1.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "data"
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 data.
- 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 data and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on data from Chapter 24. 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.
24.2 methods
methods is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 24, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For methods in Chapter 24, 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 methods to options api. 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
methods is a focused part of Vue application design in Chapter 24. 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 methods. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. methods is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 24, topic 2.
Example 2: Change one reactive value
Change one value involved in methods 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 methods 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 methods edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use methods in the task board while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. methods is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 24, topic 2.
Example 6: State ownership review
Remove duplicated state from the language selector. For 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 quiz screen has a slow request while using methods. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the methods 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 methods. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review methods in the course dashboard for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. methods is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 24, topic 2.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "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 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 methods and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on methods from Chapter 24. 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.
24.3 computed
A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 24, apply this definition specifically to computed and trace how it changes the rendered interface. In Chapter 24, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For computed in Chapter 24, 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 computed to options api. 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 computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 24, apply this definition specifically to computed and trace how it changes the rendered interface.
10 teaching examples
Example 1: Smallest useful case
Build the smallest notification center that demonstrates computed. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 24, apply this definition specifically to computed and trace how it changes the rendered interface. This is example 1 for Chapter 24, topic 3.
Example 2: Change one reactive value
Change one value involved in computed 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 computed 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 computed edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use computed in the analytics view while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 24, apply this definition specifically to computed and trace how it changes the rendered interface. This is example 5 for Chapter 24, topic 3.
Example 6: State ownership review
Remove duplicated state from the support form. For computed, 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 computed. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the computed 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 computed. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review computed in the shopping cart for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 24, apply this definition specifically to computed and trace how it changes the rendered interface. This is example 10 for Chapter 24, topic 3.
Vue code example
<script setup>
import { ref, computed } from 'vue'
const price = ref(20)
const quantity = ref(2)
const total = computed(() => price.value * quantity.value)
</script>
<template><p>Total: {{ total }}</p><button @click="quantity++">Add one</button></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by computed.
- 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 computed and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on computed from Chapter 24. 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.
24.4 watch
A watcher observes reactive state and runs side-effect logic when the watched source changes. In Chapter 24, apply this definition specifically to watch and trace how it changes the rendered interface. In Chapter 24, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For watch in Chapter 24, 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 watch to options api. 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 watcher observes reactive state and runs side-effect logic when the watched source changes. In Chapter 24, apply this definition specifically to watch and trace how it changes the rendered interface.
10 teaching examples
Example 1: Smallest useful case
Build the smallest quiz screen that demonstrates watch. Keep one input and one visible result, then explain reactive dependencies, update timing, derived values, side effects, and cleanup. A watcher observes reactive state and runs side-effect logic when the watched source changes. In Chapter 24, apply this definition specifically to watch and trace how it changes the rendered interface. This is example 1 for Chapter 24, topic 4.
Example 2: Change one reactive value
Change one value involved in watch 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 watch 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 watch edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use watch in the profile editor while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. A watcher observes reactive state and runs side-effect logic when the watched source changes. In Chapter 24, apply this definition specifically to watch and trace how it changes the rendered interface. This is example 5 for Chapter 24, topic 4.
Example 6: State ownership review
Remove duplicated state from the search panel. For watch, 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 watch. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the watch 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 watch. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review watch in the message panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. A watcher observes reactive state and runs side-effect logic when the watched source changes. In Chapter 24, apply this definition specifically to watch and trace how it changes the rendered interface. This is example 10 for Chapter 24, topic 4.
Vue code example
<script setup>
import { ref, watch } from 'vue'
const query = ref('')
watch(query, (next, previous) => console.log({ previous, next }))
</script>
<template><input v-model="query" aria-label="Search"><p>{{ query }}</p></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by watch.
- 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 watch and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on watch from Chapter 24. 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.
24.5 Lifecycle Options
Lifecycle Options is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 24, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Lifecycle Options in Chapter 24, inspect reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Keep writable state ownership explicit, derive values when possible, and separate display calculations from network, DOM, storage, timer, or other external work.
This lesson connects Lifecycle Options to options api. Start with one working case, verify the expected output, then add one edge case and explain what Vue tracks, reuses, creates, removes, or updates.
Concept in plain language
Lifecycle Options is a focused part of Vue application design in Chapter 24. 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 Lifecycle Options. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Lifecycle Options is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 24, topic 5.
Example 2: Change one reactive value
Change one value involved in Lifecycle Options 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 Lifecycle Options 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 Lifecycle Options edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Lifecycle Options in the lesson tracker while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Lifecycle Options is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 24, topic 5.
Example 6: State ownership review
Remove duplicated state from the booking form. For Lifecycle Options, 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 Lifecycle Options. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Lifecycle Options 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 Lifecycle Options. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Lifecycle Options in the notification center for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Lifecycle Options is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 24, topic 5.
Vue code example
<script setup>
import { ref } from 'vue'
const topic = "Lifecycle Options"
const active = ref(false)
</script>
<template>
<section><h2>{{ topic }}</h2><button :aria-pressed="active" @click="active=!active">Toggle state</button><p>{{ active ? 'Active' : 'Inactive' }}</p></section>
</template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Lifecycle Options.
- Read the reactive state, props, route/store input, or injected value before the template.
- Trace the event, dependency, watcher, lifecycle hook, or navigation action that changes the display.
- Test one normal path and one edge case, including cleanup when external work is involved.
- Confirm accessibility, mobile width, and RTL behavior for user-facing controls and translated text.
Expected behavior: A small Vue interface demonstrates Lifecycle Options and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Lifecycle Options from Chapter 24. 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 24 review — 10 questions and answers
1. What is the purpose of data?
Answer: data is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
2. What should you inspect when data 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 methods?
Answer: methods is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
4. What should you inspect when 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.
5. What is the purpose of computed?
Answer: A computed property derives a cached value from reactive dependencies and updates when those dependencies change. In Chapter 24, apply this definition specifically to computed and trace how it changes the rendered interface.
6. What should you inspect when computed behaves unexpectedly?
Answer: Inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Reduce the feature to a small component and trace reactive input through the rendered result.
7. What is the purpose of watch?
Answer: A watcher observes reactive state and runs side-effect logic when the watched source changes. In Chapter 24, apply this definition specifically to watch and trace how it changes the rendered interface.
8. What should you inspect when watch behaves unexpectedly?
Answer: Inspect reactive dependencies, update timing, derived values, side effects, and cleanup. Reduce the feature to a small component and trace reactive input through the rendered result.
9. What is the purpose of Lifecycle Options?
Answer: Lifecycle Options is a focused part of Vue application design in Chapter 24. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10. What should you inspect when Lifecycle Options 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.