Error boundaries with onErrorCaptured in Vue

Introduction

Error boundaries help catch and handle errors in parts of your Vue app so the whole app doesn't break.

When you want to show a friendly message if a part of your app crashes.

When you want to log errors from child components for debugging.

When you want to prevent one component's error from stopping the whole page.

When you want to recover gracefully from errors in specific UI sections.

Syntax

Vue

<script setup>
import { onErrorCaptured } from 'vue'

onErrorCaptured((error, instance, info) => {
  // handle or log the error
  return false // to stop error propagation
})
</script>

onErrorCaptured is a Vue Composition API hook to catch errors in child components.

Returning false stops the error from propagating further up.

Examples

Catches errors and logs the message, then stops propagation.

Vue

<script setup>
import { onErrorCaptured } from 'vue'

onErrorCaptured((error) => {
  console.error('Error caught:', error.message)
  return false
})
</script>

Shows an alert with info about where the error happened.

Vue

<script setup>
import { onErrorCaptured } from 'vue'

onErrorCaptured((error, instance, info) => {
  alert(`Error in component: ${info}`)
  return false
})
</script>

Returns true to let the error continue propagating to parent handlers.

Vue

<script setup>
import { onErrorCaptured } from 'vue'

onErrorCaptured(() => {
  // ignore error and let it propagate
  return true
})
</script>

Sample Program

This example shows a component that throws an error immediately. The ErrorBoundary catches it and shows a red error message instead of breaking the whole app.

Vue

<template>
  <ErrorBoundary>
    <BuggyComponent />
  </ErrorBoundary>
</template>

<script setup>
import { defineComponent, ref, onErrorCaptured } from 'vue'

const BuggyComponent = defineComponent({
  setup() {
    const count = ref(0)
    if (count.value === 0) {
      throw new Error('Oops! BuggyComponent crashed.')
    }
    return { count }
  },
  template: `<div>Count: {{ count }}</div>`
})

const ErrorBoundary = defineComponent({
  setup(props, { slots }) {
    const errorMessage = ref('')

    onErrorCaptured((error) => {
      errorMessage.value = error.message
      return false
    })

    return () => errorMessage.value
      ? <div role="alert" aria-live="assertive" style="color: red; font-weight: bold;">Error: {errorMessage.value}</div>
      : slots.default()
  }
})
</script>

Important Notes

Use onErrorCaptured inside a component to catch errors from its children.

Always provide a fallback UI to keep your app usable when errors happen.

Remember to add role="alert" and aria-live="assertive" for accessibility when showing error messages.

Summary

Error boundaries catch errors in child components to prevent app crashes.

onErrorCaptured hook lets you handle errors in Vue's Composition API.

Return false to stop error propagation and show fallback UI.

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