Error boundaries with onErrorCaptured in Vue - Mini Project: Build & Apply

Error boundaries with onErrorCaptured in Vue

📖 Scenario: You are building a Vue app that shows user profiles. Sometimes, a profile might have missing or broken data that causes errors. You want to catch these errors gracefully and show a friendly message instead of a broken page.

🎯 Goal: Create a Vue component that uses onErrorCaptured to catch errors from a child component and display a fallback message.

📋 What You'll Learn

Create a child component called UserProfile that throws an error when the user prop is missing.

Create a parent component called ErrorBoundary that uses onErrorCaptured to catch errors from UserProfile.

Show a fallback message inside ErrorBoundary when an error is caught.

Pass a user prop to UserProfile from ErrorBoundary.

💡 Why This Matters

🌍 Real World

Error boundaries help keep your app running smoothly by catching unexpected errors in parts of your UI and showing friendly messages instead of crashing the whole page.

💼 Career

Understanding error boundaries is important for building robust Vue applications that handle failures gracefully and improve user experience.

1

Create the UserProfile component

Create a Vue component called UserProfile that accepts a prop named user. If user is not provided, throw an error with the message 'User data is missing'. Otherwise, render a <div> showing User: {{ user.name }}.

Vue

// Create UserProfile component with user prop and error throw


  

Hint

Use defineProps to declare the user prop. Check if user is missing and throw an error. Render the user's name inside a <div>.

2

Create the ErrorBoundary component setup

Create a Vue component called ErrorBoundary. Inside <script setup>, import ref and onErrorCaptured from 'vue'. Create a reactive variable called error initialized to null. Use onErrorCaptured to catch errors and set error.value to the error message.

Vue

// Import ref and onErrorCaptured
// Create error ref initialized to null
// Use onErrorCaptured to set error.value


  

Hint

Use ref(null) to create error. Use onErrorCaptured callback to catch errors and update error.value.

3

Render UserProfile and show fallback on error

Inside the ErrorBoundary template, use a <template> with v-if to show a <div> with text 'Error: ' + error if error is not null. Otherwise, render the UserProfile component and pass a user prop with value { name: 'Alice' }. Import UserProfile at the top.

Vue

import { ref, onErrorCaptured } from 'vue'
// Import UserProfile component
const error = ref(null)
onErrorCaptured((err) => {
  error.value = err.message
  return false
})


  

Hint

Use v-if to show the error message. Use v-else to show UserProfile with the user prop.

4

Test error handling by passing no user

Modify the ErrorBoundary template to render UserProfile without the user prop to trigger the error. Keep the error message display logic unchanged.

Vue

import { ref, onErrorCaptured } from 'vue'
import UserProfile from './UserProfile.vue'
const error = ref(null)
onErrorCaptured((err) => {
  error.value = err.message
  return false
})


  

Hint

Remove the user prop from UserProfile to cause the error and see the fallback message.

Practice

1. What is the main purpose of the onErrorCaptured hook in Vue?

easy

A. To prevent any rendering of child components

B. To automatically reload the page when an error occurs

C. To log errors only in the browser console without affecting UI

D. To catch errors from child components and handle them gracefully

Solution

1. Step 1: Understand the role of error boundaries

   Error boundaries catch errors in child components to prevent the whole app from crashing.

2. Step 2: Identify what onErrorCaptured does

   This hook lets you catch those errors and handle them, for example by showing fallback UI.

3. Final Answer:

   To catch errors from child components and handle them gracefully -> Option D

4. Quick Check:

   Catches child errors gracefully [OK]

Hint: Remember: onErrorCaptured catches child errors for graceful handling [OK]

Common Mistakes:

• Thinking it reloads the page automatically
• Believing it blocks all child rendering
• Assuming it only logs errors without UI impact

2. Which of the following is the correct way to use onErrorCaptured in a Vue 3 Composition API setup function?

easy

A. onErrorCaptured.handleError(error => { /* handle error */ })

B. onErrorCaptured((error, instance, info) => { /* handle error */ })

C. setup() { onErrorCaptured: function(error) { /* handle error */ } }

D. onErrorCaptured = (error) => { /* handle error */ }

Solution

1. Step 1: Recall the correct syntax for hooks in Composition API

   Hooks like onErrorCaptured are called as functions with a callback.

2. Step 2: Match the syntax with options

   onErrorCaptured((error, instance, info) => { /* handle error */ }) correctly shows calling onErrorCaptured with a callback function receiving error details.

3. Final Answer:

   onErrorCaptured((error, instance, info) => { /* handle error */ }) -> Option B

4. Quick Check:

   Hook usage = function call with callback [OK]

Hint: Hooks are functions called with callbacks in setup() [OK]

Common Mistakes:

• Assigning onErrorCaptured instead of calling it
• Using object syntax inside setup incorrectly
• Calling non-existent methods on onErrorCaptured

3. Given this Vue component snippet, what will be the console output when ChildComponent throws an error?

setup() {
  onErrorCaptured((err) => {
    console.log('Error caught:', err.message)
    return false
  })
}

medium

A. Error caught: [error message]

B. No output, error is ignored

C. Error caught: [error message] and error propagates further

D. Runtime error: onErrorCaptured not defined

Solution

1. Step 1: Understand onErrorCaptured behavior with return false

   Returning false stops error propagation and prevents further bubbling.

2. Step 2: Analyze console.log call

   The callback logs the error message, so console shows 'Error caught:' plus the error message.

3. Final Answer:

   Error caught: [error message] -> Option A

4. Quick Check:

   Return false stops propagation, logs error [OK]

Hint: Return false in onErrorCaptured stops error bubbling [OK]

Common Mistakes:

• Assuming error propagates despite return false
• Expecting no console output
• Confusing syntax causing runtime errors

4. Identify the error in this Vue 3 setup function using onErrorCaptured:

setup() {
  onErrorCaptured = (error) => {
    console.error(error)
    return false
  }
}

medium

A. Incorrect assignment instead of calling onErrorCaptured as a function

B. Missing import of onErrorCaptured from Vue

C. Returning false is not allowed in onErrorCaptured

D. console.error cannot be used inside setup

Solution

1. Step 1: Check how onErrorCaptured is used

   It should be called as a function with a callback, not assigned to a function.

2. Step 2: Identify the incorrect syntax

   The code assigns a function to onErrorCaptured instead of calling it, causing an error.

3. Final Answer:

   Incorrect assignment instead of calling onErrorCaptured as a function -> Option A

4. Quick Check:

   Hooks are called, not assigned [OK]

Hint: Use onErrorCaptured(callback), not assignment [OK]

Common Mistakes:

• Assigning hook instead of calling it
• Forgetting to import onErrorCaptured
• Misunderstanding return false usage

5. You want to create an error boundary component in Vue 3 that catches errors from its children and shows a fallback message. Which approach correctly uses onErrorCaptured to stop error propagation and display fallback UI?

hard

A. Wrap children in try-catch inside template to catch errors

B. Use onErrorCaptured but do not return anything, so errors propagate

C. Use onErrorCaptured to set a reactive error state and return false to stop propagation

D. Use onErrorCaptured and always return true to propagate errors

Solution

1. Step 1: Understand error boundary behavior

   An error boundary catches errors and shows fallback UI by tracking error state.

2. Step 2: Use onErrorCaptured to update error state and stop propagation

   Returning false in onErrorCaptured stops error bubbling, allowing fallback UI to show.

3. Final Answer:

   Use onErrorCaptured to set a reactive error state and return false to stop propagation -> Option C

4. Quick Check:

   Set error state + return false = error boundary [OK]

Hint: Return false in onErrorCaptured to stop error bubbling [OK]

Common Mistakes:

• Not returning false, so errors keep propagating
• Trying to catch errors in template with try-catch
• Returning true which continues error propagation