Component registration (global vs local) in Vue

Introduction

Component registration lets Vue know about your components so you can use them in your app. Global registration makes components available everywhere, while local registration limits them to specific parts.

You want a button component used in many places across your app.

You have a special widget used only inside one page or component.

You want to keep your app organized by only loading components where needed.

You want to reduce app size by not registering unused components globally.

Syntax

Vue

/* Global registration */
import MyButton from './MyButton.vue'
app.component('MyButton', MyButton)

/* Local registration inside a component */
export default {
  components: {
    MyButton
  }
}

Global registration is done on the Vue app instance before mounting.

Local registration is done inside the components option of a component.

Examples

This makes <MyButton> usable anywhere in the app without importing it again.

Vue

// Global registration example
import { createApp } from 'vue'
import App from './App.vue'
import MyButton from './MyButton.vue'

const app = createApp(App)
app.component('MyButton', MyButton)
app.mount('#app')

This makes <MyButton> usable only inside this component.

Vue

// Local registration example
import MyButton from './MyButton.vue'

export default {
  components: {
    MyButton
  },
  template: `<MyButton />`
}

Sample Program

This example shows a button component registered locally inside a parent component. Clicking the button updates the count shown inside it.

Vue

<script setup>
import { ref } from 'vue'
import MyButton from './MyButton.vue'

const count = ref(0)
function increment() {
  count.value++
}
</script>

<template>
  <h2>Local Registration Example</h2>
  <MyButton @click="increment">Clicked {{ count }} times</MyButton>
</template>

<!-- MyButton.vue -->
<script setup>
const emit = defineEmits(['click'])
</script>
<template>
  <button @click="$emit('click')" style="padding: 0.5rem 1rem; font-size: 1rem;">
    <slot></slot>
  </button>
</template>

Important Notes

Global registration can increase app size if many components are registered but not used everywhere.

Local registration helps keep components scoped and can improve performance by loading only needed components.

Use PascalCase or kebab-case for component names consistently.

Summary

Global registration makes components available everywhere in the app.

Local registration limits component usage to a specific component only.

Choose registration type based on how widely you use the component and app size considerations.

Practice

1. What is the main difference between global and local component registration in Vue?

easy

A. Global registration requires importing components manually, local does not.

B. Local registration makes a component available everywhere, global limits it to one component.

C. Global registration makes a component available everywhere, local limits it to one component.

D. Local registration automatically registers components globally.

Solution

1. Step 1: Understand global registration

   Global registration means the component can be used in any template without importing it again.

2. Step 2: Understand local registration

   Local registration means the component is only available inside the component where it is registered.

3. Final Answer:

   Global registration makes a component available everywhere, local limits it to one component. -> Option C

4. Quick Check:

   Global = everywhere, Local = one component [OK]

Hint: Global = everywhere, local = one place only [OK]

Common Mistakes:

• Confusing global with local availability
• Thinking local registration is automatic
• Assuming global requires manual import every time

2. Which of the following is the correct syntax to register a component locally inside a Vue component?

easy

A. export default { globalComponents: { MyComponent } }

B. Vue.component('MyComponent', MyComponent)

C. import MyComponent from './MyComponent.vue';

D. components: { MyComponent }

Solution

1. Step 1: Identify local registration syntax

   Local registration uses the components option inside the component definition object.

2. Step 2: Match correct syntax

   The syntax is components: { MyComponent } to register locally.

3. Final Answer:

   components: { MyComponent } -> Option D

4. Quick Check:

   Local registration uses components: { } [OK]

Hint: Local registration uses components: { ComponentName } [OK]

Common Mistakes:

• Using Vue.component() for local registration
• Confusing import statement with registration
• Trying to use globalComponents option which doesn't exist

3. Given this code, what will be the output when rendering <ParentComponent/>?

const ChildComponent = {
  template: '
Child here
'
}

const ParentComponent = {
  template: '
',
  components: { ChildComponent }
}

app.component('parent-component', ParentComponent)
app.mount('#app')

medium

A. Child here

B. Error: Unknown custom element

C.

D. Child here

Solution

1. Step 1: Check local registration in ParentComponent

   ChildComponent is registered locally inside ParentComponent using components: { ChildComponent }.

2. Step 2: Understand template rendering

   The tag inside ParentComponent's template will render ChildComponent's template

   Child here

   only if the tag name matches the registered component name in kebab-case.

3. Step 3: Identify the issue

   The component is registered as ChildComponent but used as , which Vue treats as a different tag. Since 'child-component' is not globally registered, Vue will throw an unknown custom element error.

4. Final Answer:

   Error: Unknown custom element <child-component> -> Option B

5. Quick Check:

   Component names are case-sensitive and must match usage [OK]

Hint: Component names must match tag names exactly or use kebab-case [OK]

Common Mistakes:

• Assuming PascalCase component names automatically match kebab-case tags
• Forgetting to register components globally when using kebab-case tags
• Expecting local registration to work with mismatched tag names

4. What is wrong with this Vue code snippet?

const app = Vue.createApp({})

app.component('MyButton', {
  template: 'Click me'
})

const AnotherComponent = {
  template: ''
}

app.component('AnotherComponent', AnotherComponent)

app.mount('#app')

medium

A. The tag inside AnotherComponent template should be lowercase .

B. MyButton component is not registered globally.

C. AnotherComponent is missing local registration of MyButton.

D. Vue.createApp() cannot register components.

Solution

1. Step 1: Check component registration

   MyButton is registered globally using app.component('MyButton', ...), so it is available everywhere.

2. Step 2: Check template tag casing

   Vue requires component tags in templates to be kebab-case or PascalCase but HTML is case-insensitive, so should be .

3. Final Answer:

   The <MyButton /> tag inside AnotherComponent template should be lowercase <my-button />. -> Option A

4. Quick Check:

   Component tags must be kebab-case in templates [OK]

Hint: Use kebab-case for component tags in templates [OK]

Common Mistakes:

• Using PascalCase tags directly in templates
• Thinking global registration needs import in every component
• Assuming Vue.createApp() can't register components

5. You have a button component used in many places and a modal component used only inside one page component. How should you register them for best practice?

hard

A. Register the button component globally and the modal component locally inside the page component.

B. Register both components globally for consistency.

C. Register both components locally inside each component that uses them.

D. Register the modal component globally and the button component locally.

Solution

1. Step 1: Consider usage frequency

   The button is used many places, so global registration avoids repeated imports and registrations.

2. Step 2: Consider component scope

   The modal is used only inside one page component, so local registration keeps scope limited and reduces global clutter.

3. Final Answer:

   Register the button component globally and the modal component locally inside the page component. -> Option A

4. Quick Check:

   Global for many uses, local for few uses [OK]

Hint: Global for shared, local for limited use components [OK]

Common Mistakes:

• Registering rarely used components globally unnecessarily
• Registering widely used components locally repeatedly
• Ignoring app size and performance considerations