Vue.js • Chapter 37 • Foundations to Advanced
Navigation Guards
Each topic includes substantial explanation, ten focused examples, its own Vue code example, step-by-step reasoning, expected behavior, and practice.
37.1 Global Guards
Global Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 37, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Global Guards in Chapter 37, 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 Global Guards to navigation guards. 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
Global Guards is a focused part of Vue application design in Chapter 37. 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 photo gallery that demonstrates Global Guards. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Global Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 37, topic 1.
Example 2: Change one reactive value
Change one value involved in Global Guards inside the notification center. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Global Guards across two components in the task board. 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 language selector. Handle the Global Guards edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Global Guards in the quiz screen while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Global Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 37, topic 1.
Example 6: State ownership review
Remove duplicated state from the analytics view. For Global Guards, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the support form has a slow request while using Global Guards. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Global Guards responsibility from a crowded course dashboard into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the profile editor before optimizing Global Guards. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Global Guards in the search panel for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Global Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 37, topic 1.
Vue code example
<script setup>
import { useRoute, useRouter } from 'vue-router'
const route = useRoute()
const router = useRouter()
function goHome(){ router.push('/') }
</script>
<template><p>Route: {{ route.fullPath }}</p><button @click="goHome">Home</button></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Global Guards.
- 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 Global Guards and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Global Guards from Chapter 37. 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.
37.2 Per-Route Guards
Per-Route Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 37, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Per-Route Guards in Chapter 37, inspect URL state, route parameters, matched records, navigation lifecycle, and failure states. 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 Per-Route Guards to navigation guards. 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
Per-Route Guards is a focused part of Vue application design in Chapter 37. 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 language selector that demonstrates Per-Route Guards. Keep one input and one visible result, then explain URL state, route parameters, matched records, navigation lifecycle, and failure states. Per-Route Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 37, topic 2.
Example 2: Change one reactive value
Change one value involved in Per-Route Guards inside the quiz screen. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Per-Route Guards across two components in the analytics view. 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 support form. Handle the Per-Route Guards edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Per-Route Guards in the course dashboard while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Per-Route Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 37, topic 2.
Example 6: State ownership review
Remove duplicated state from the profile editor. For Per-Route Guards, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the search panel has a slow request while using Per-Route Guards. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Per-Route Guards responsibility from a crowded shopping cart into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the lesson tracker before optimizing Per-Route Guards. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Per-Route Guards in the booking form for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Per-Route Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 37, topic 2.
Vue code example
<script setup>
import { useRoute, useRouter } from 'vue-router'
const route = useRoute()
const router = useRouter()
function goHome(){ router.push('/') }
</script>
<template><p>Route: {{ route.fullPath }}</p><button @click="goHome">Home</button></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Per-Route Guards.
- 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 Per-Route Guards and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Per-Route Guards from Chapter 37. 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.
37.3 In-Component Guards
In-Component Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 37, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For In-Component Guards in Chapter 37, 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 In-Component Guards to navigation guards. 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
In-Component Guards is a focused part of Vue application design in Chapter 37. 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 support form that demonstrates In-Component Guards. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. In-Component Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 37, topic 3.
Example 2: Change one reactive value
Change one value involved in In-Component Guards inside the course dashboard. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use In-Component Guards across two components in the profile editor. 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 search panel. Handle the In-Component Guards edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use In-Component Guards in the shopping cart while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. In-Component Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 37, topic 3.
Example 6: State ownership review
Remove duplicated state from the lesson tracker. For In-Component Guards, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the booking form has a slow request while using In-Component Guards. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the In-Component Guards responsibility from a crowded message panel into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the admin table before optimizing In-Component Guards. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review In-Component Guards in the photo gallery for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. In-Component Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 37, topic 3.
Vue code example
<script setup>
import { useRoute, useRouter } from 'vue-router'
const route = useRoute()
const router = useRouter()
function goHome(){ router.push('/') }
</script>
<template><p>Route: {{ route.fullPath }}</p><button @click="goHome">Home</button></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by In-Component Guards.
- 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 In-Component Guards and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on In-Component Guards from Chapter 37. 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.
37.4 Redirects
Redirects is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 37, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Redirects in Chapter 37, 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 Redirects to navigation guards. 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
Redirects is a focused part of Vue application design in Chapter 37. 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 search panel that demonstrates Redirects. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Redirects is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 37, topic 4.
Example 2: Change one reactive value
Change one value involved in Redirects inside the shopping cart. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Redirects across two components in the lesson tracker. 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 booking form. Handle the Redirects edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Redirects in the message panel while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Redirects is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 37, topic 4.
Example 6: State ownership review
Remove duplicated state from the admin table. For Redirects, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the photo gallery has a slow request while using Redirects. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Redirects responsibility from a crowded notification center into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the task board before optimizing Redirects. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Redirects in the language selector for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Redirects is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 37, topic 4.
Vue code example
<script setup>
import { useRoute, useRouter } from 'vue-router'
const route = useRoute()
const router = useRouter()
function goHome(){ router.push('/') }
</script>
<template><p>Route: {{ route.fullPath }}</p><button @click="goHome">Home</button></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Redirects.
- 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 Redirects and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Redirects from Chapter 37. 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.
37.5 Guard Error Handling
Guard Error Handling is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. In Chapter 37, trace the value or control flow from its source to the rendered interface so you can explain why Vue changes the screen.
For Guard Error Handling in Chapter 37, 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 Guard Error Handling to navigation guards. 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
Guard Error Handling is a focused part of Vue application design in Chapter 37. 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 booking form that demonstrates Guard Error Handling. Keep one input and one visible result, then explain reactive inputs, component ownership, rendered output, edge cases, and what causes another update. Guard Error Handling is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 1 for Chapter 37, topic 5.
Example 2: Change one reactive value
Change one value involved in Guard Error Handling inside the message panel. Predict what Vue will update before running it, then compare the prediction with the rendered result.
Example 3: Parent-child comparison
Use Guard Error Handling across two components in the admin table. 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 photo gallery. Handle the Guard Error Handling edge case explicitly instead of leaving stale output.
Example 5: Accessibility review
Use Guard Error Handling in the notification center while checking semantic HTML, labels, focus order, keyboard access, and understandable status feedback. Guard Error Handling is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 5 for Chapter 37, topic 5.
Example 6: State ownership review
Remove duplicated state from the task board. For Guard Error Handling, derive values when possible and keep the writable source with the component or store that owns it.
Example 7: Slow-network scenario
Assume the language selector has a slow request while using Guard Error Handling. Decide what remains interactive, what shows pending feedback, and how stale responses are prevented.
Example 8: Refactoring exercise
Extract the Guard Error Handling responsibility from a crowded quiz screen into a focused component or composable with a narrow API.
Example 9: Performance experiment
Measure the analytics view before optimizing Guard Error Handling. Check reactive work, repeated calculations, list size, component updates, and user-visible delay.
Example 10: Production review
Review Guard Error Handling in the support form for errors, security, localization, RTL, narrow screens, accessibility, and what monitoring should report. Guard Error Handling is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements. This is example 10 for Chapter 37, topic 5.
Vue code example
<script setup>
import { useRoute, useRouter } from 'vue-router'
const route = useRoute()
const router = useRouter()
function goHome(){ router.push('/') }
</script>
<template><p>Route: {{ route.fullPath }}</p><button @click="goHome">Home</button></template>Step-by-step code explanation
- Identify the Vue responsibility demonstrated by Guard Error Handling.
- 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 Guard Error Handling and updates according to the interaction or data in the example.
Practice exercise
Create a small Vue feature focused on Guard Error Handling from Chapter 37. 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 37 review — 10 questions and answers
1. What is the purpose of Global Guards?
Answer: Global Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
2. What should you inspect when Global Guards 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 Per-Route Guards?
Answer: Per-Route Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
4. What should you inspect when Per-Route Guards behaves unexpectedly?
Answer: Inspect URL state, route parameters, matched records, navigation lifecycle, and failure states. Reduce the feature to a small component and trace reactive input through the rendered result.
5. What is the purpose of In-Component Guards?
Answer: In-Component Guards is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
6. What should you inspect when In-Component Guards 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 Redirects?
Answer: Redirects is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
8. What should you inspect when Redirects 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 Guard Error Handling?
Answer: Guard Error Handling is a focused part of Vue application design in Chapter 37. Study its inputs, reactive dependencies, component ownership, rendered result, edge cases, and cleanup requirements.
10. What should you inspect when Guard Error Handling 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.