Compound components pattern in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Compound Components Pattern in Vue?

It is a design pattern where a parent component controls the state and logic, while child components handle the UI. They work together to create flexible and reusable components.

intermediate

How do child components communicate with the parent in the Compound Components Pattern?

Child components use Vue's provide/inject or slots to access the parent's state and methods, allowing them to stay in sync without prop drilling.

beginner

Why use the Compound Components Pattern instead of passing props directly?

It keeps the API clean and flexible, avoids passing many props through layers, and allows children to share state easily with the parent.

intermediate

Which Vue feature is commonly used to implement Compound Components?

The <slot> element is used to place child components inside the parent, and provide/inject is used to share state and methods.

beginner

Give an example of a real-life analogy for the Compound Components Pattern.

Think of a TV remote (parent) controlling the TV (children). The remote manages the state (channel, volume), and buttons (children) send commands but don’t hold state themselves.

In Vue's Compound Components Pattern, how do child components usually get access to shared state?

A Using provide/inject or slots

B By emitting events only

C By fetching data from API directly

D By using global variables

Child components use provide/inject or slots to access shared state from the parent, avoiding prop drilling.

What is the main benefit of using Compound Components Pattern?

A It makes components tightly coupled

B It simplifies state sharing and keeps API clean

C It requires more props to be passed

D It avoids using slots

Compound Components Pattern simplifies sharing state and keeps the component API clean and flexible.

Which Vue feature helps place child components inside a parent component's template?

A <slot> element

B v-for directive

C v-if directive

D watch property

The element allows child components to be inserted into the parent's template.

In the Compound Components Pattern, who controls the state?

A Vuex store only

B Child components

C Parent component

D No one controls state

The parent component controls the shared state, while children focus on UI.

Which of these is NOT a typical use case for Compound Components?

A Form controls with shared validation

B Dropdown menus with Menu and MenuItem

C Tabs with TabList and TabPanels

D Isolated components with no shared state

Compound Components are used when components share state; isolated components don’t need this pattern.

Explain how the Compound Components Pattern works in Vue and why it is useful.

Think about how a parent and children share data and responsibilities.

Describe a simple example of a compound component in Vue and how the parts communicate.

Imagine a tabs component with tab buttons and content panels.

Practice

1. What is the main purpose of the compound components pattern in Vue?

easy

A. To group related UI parts inside one main component for better organization

B. To create multiple unrelated components in one file

C. To avoid using provide and inject for state sharing

D. To write components without any communication between them

Solution

1. Step 1: Understand the pattern goal

   The compound components pattern groups related UI parts to work together inside one main component.

2. Step 2: Compare options

   Only To group related UI parts inside one main component for better organization correctly describes grouping related UI parts for better organization and communication.

3. Final Answer:

   To group related UI parts inside one main component for better organization -> Option A

4. Quick Check:

   Compound components group related parts = B [OK]

Hint: Think: grouping related UI parts inside one component [OK]

Common Mistakes:

• Confusing unrelated components grouping
• Ignoring state sharing between parts
• Thinking it avoids provide/inject

2. Which Vue feature is commonly used to share state between compound components?

easy

A. provide and inject

B. props

C. v-model

D. emit events

Solution

1. Step 1: Identify state sharing methods

   Vue offers several ways to share data, but for compound components, provide and inject are designed for parent-child communication without prop drilling.

2. Step 2: Match pattern usage

   Compound components use provide/inject to share state internally, unlike props or emit which are for direct parent-child or event communication.

3. Final Answer:

   provide and inject -> Option A

4. Quick Check:

   State sharing in compound components = provide/inject [OK]

Hint: Remember: provide/inject share state inside compound components [OK]

Common Mistakes:

• Choosing props which require manual passing
• Confusing emit with state sharing
• Thinking v-model is for internal state sharing

3. Given this Vue compound component setup, what will be the rendered output?

const TabGroup = {
  setup() {
    provide('activeTab', ref('home'))
  },
  template: `
`
}

const Tab = {
  inject: ['activeTab'],
  props: ['name'],
  template: `{{ name }}`
}

// Usage:
// 
//   
//   
// 

medium

A. homeprofile

B. homeprofile

C. homeprofile

D. Error: activeTab is not reactive

Solution

1. Step 1: Understand provide/inject in Options API

   TabGroup provides 'activeTab' as ref('home'). Tab injects ['activeTab'], receiving the ref object (not auto-unwrapped in Options API).

2. Step 2: Evaluate rendering logic

   In template, activeTab (ref object) === name (string) is always false. No 'active' class applied to either button.

3. Final Answer:

   <button>home</button><button>profile</button> -> Option B

4. Quick Check:

   Options API inject ref === string = false [OK]

Hint: Options API inject returns ref object, not value [OK]

Common Mistakes:

• Assuming inject returns raw value, not ref
• Confusing which tab is active
• Thinking activeTab is not reactive

4. What is the main issue in this compound component code?

const Dropdown = {
  setup() {
    const open = ref(false)
    provide('open', open)
  },
  template: `
`
}

const DropdownToggle = {
  inject: ['open'],
  template: `Toggle`
}

medium

A. The provide key 'open' is missing

B. The template syntax is invalid

C. The 'open' variable is not returned from setup in Dropdown

D. The 'open' ref is not reactive inside DropdownToggle

Solution

1. Step 1: Check inject handling in Options API

   Injected refs via inject: ['open'] are not auto-unwrapped in Options API templates. 'open' is the ref object.

2. Step 2: Understand mutation and reactivity issue

   @click="open = !open" reassigns a boolean to the ref variable (breaks link to original ref) and lacks .value access, making the ref unusable reactively as boolean state.

3. Final Answer:

   The 'open' ref is not reactive inside DropdownToggle -> Option D

4. Quick Check:

   Options API injected ref needs .value [OK]

Hint: Use .value for injected refs in Options API templates [OK]

Common Mistakes:

• Thinking provider setup needs to return state for provide
• Template syntax looks invalid
• Provide key seems missing

5. You want to build a compound Tabs component where clicking a tab updates the active tab and content changes accordingly. Which approach correctly implements this pattern in Vue 3?

hard

A. Use local state in each Tab component without sharing activeTab

B. Pass activeTab as prop to each Tab and emit events to Tabs to update state

C. Use provide to share activeTab ref in Tabs, inject in TabList and TabPanels, update activeTab on Tab click

D. Use global event bus to communicate active tab changes between components

Solution

1. Step 1: Identify compound components pattern usage

   The pattern uses provide/inject to share state like activeTab across nested components without prop drilling.

2. Step 2: Evaluate options for state management

   Use provide to share activeTab ref in Tabs, inject in TabList and TabPanels, update activeTab on Tab click correctly uses provide to share activeTab ref and inject in child components, updating activeTab on tab click to reflect changes.

3. Final Answer:

   Use provide to share activeTab ref in Tabs, inject in TabList and TabPanels, update activeTab on Tab click -> Option C

4. Quick Check:

   Compound components share state via provide/inject = D [OK]

Hint: Use provide/inject to share and update active tab state [OK]

Common Mistakes:

• Using props and events causing complex prop drilling
• Using global event bus which is not recommended
• Keeping state local in each tab causing no sync