Higher-order components concept in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a higher-order component that wraps a base component.

Vue

<script setup>
import BaseComponent from './BaseComponent.vue'

const withWrapper = (Component) => {
  return {
    components: { Component },
    template: `<div class=\"wrapper\"><[1] /></div>`
  }
}

const WrappedComponent = withWrapper(BaseComponent)
</script>

Drag options to blanks, or click blank then click option'

AwithWrapper

BBaseComponent

CComponent

Dwrapper

Attempts:

3 left

💡 Hint

Common Mistakes

Using the base component name instead of the parameter 'Component'.

Using the wrapper class name instead of the component name.

The higher-order component returns a new component that renders the passed Component inside a wrapper div. The blank should be filled with Component to render it.

2fill in blank

medium

Complete the code to pass props from the higher-order component to the wrapped component.

Vue

<script setup>
import BaseComponent from './BaseComponent.vue'

const withWrapper = (Component) => {
  return {
    components: { Component },
    props: ['msg'],
    template: `<div class=\"wrapper\"><Component :msg=[1] /></div>`
  }
}

const WrappedComponent = withWrapper(BaseComponent)
</script>

Drag options to blanks, or click blank then click option'

Amsg

B$props.msg

Cprops.msg

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using an undefined variable like 'message' instead of 'msg'.

Trying to access props with '$props' which is not available in this template syntax.

The higher-order component receives a prop named msg and passes it down to the wrapped component using :msg="msg". The blank should be filled with msg to bind the prop correctly.

3fill in blank

hard

Fix the error in the higher-order component by completing the code to correctly define the component's setup function.

Vue

<script setup>
import BaseComponent from './BaseComponent.vue'

const withWrapper = (Component) => {
  return {
    components: { Component },
    setup() {
      const message = 'Hello from HOC'
      return { [1] }
    },
    template: `<div><Component :msg=\"message\" /></div>`
  }
}

const WrappedComponent = withWrapper(BaseComponent)
</script>

Drag options to blanks, or click blank then click option'

Aprops.message

B{ message }

Creturn message

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the variable directly instead of an object.

Trying to access props.message which is not defined here.

The setup function must return an object with the properties to expose to the template. Returning { message } exposes the message variable.

4fill in blank

hard

Fill both blanks to create a higher-order component that adds a click counter to the wrapped component.

Vue

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

const withClickCounter = (Component) => {
  return {
    components: { Component },
    setup() {
      const count = ref(0)
      const increment = () => count.value++
      return { count, [1] }
    },
    template: `<div><Component @click=[2] :count=\"count\" /></div>`
  }
}

const EnhancedButton = withClickCounter(BaseButton)
</script>

Drag options to blanks, or click blank then click option'

Aincrement

Bcount

Cincrement()

DincrementCount

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the count variable instead of the increment function.

Calling the function in the template instead of passing the function reference.

The setup function returns increment to expose the click handler. The template binds the @click event to increment to increase the count.

5fill in blank

hard

Fill all three blanks to create a higher-order component that logs a message when the wrapped component is mounted and passes a prop.

Vue

<script setup>
import { onMounted } from 'vue'
import BaseCard from './BaseCard.vue'

const withLogger = (Component) => {
  return {
    components: { Component },
    props: ['title'],
    setup(props) {
      const title = props.title
      onMounted(() => {
        console.log([1])
      })
      return { [2] }
    },
    template: `<div><Component :title=[3] /></div>`
  }
}

const LoggedCard = withLogger(BaseCard)
</script>

Drag options to blanks, or click blank then click option'

A'Component mounted!'

Btitle

Cprops.title

Attempts:

3 left

💡 Hint

Common Mistakes

Logging the prop instead of a string message.

Returning props.title instead of the prop name.

Binding the prop incorrectly in the template.

The onMounted hook logs a message string. The setup returns title to expose the prop. The template binds the title prop to the wrapped component.

Practice

1. What is the main purpose of a higher-order component (HOC) in Vue?

easy

A. To create a new Vue instance from scratch

B. To replace the Vue router with a new navigation system

C. To wrap a component and add shared logic or styling

D. To directly manipulate the DOM elements inside a component

Solution

1. Step 1: Understand what HOCs do

   Higher-order components wrap existing components to add extra features without changing the original component.

2. Step 2: Identify the correct purpose

   Among the options, only wrapping a component to add shared logic or styling matches the HOC concept.

3. Final Answer:

   To wrap a component and add shared logic or styling -> Option C

4. Quick Check:

   HOC purpose = wrap and add logic [OK]

Hint: HOCs wrap components to add features without changing them [OK]

Common Mistakes:

• Confusing HOCs with routing or Vue instance creation
• Thinking HOCs manipulate DOM directly
• Believing HOCs replace components instead of wrapping

2. Which of the following is the correct syntax to create a higher-order component in Vue 3 using the Composition API?

easy

A. const withLogger = (WrappedComponent) => { return { setup() { return () => h(WrappedComponent) } } }

B. const withLogger = (WrappedComponent) => { return WrappedComponent.setup() }

C. const withLogger = (WrappedComponent) => { return new Vue({ render: () => h(WrappedComponent) }) }

D. const withLogger = (WrappedComponent) => { return () => WrappedComponent }

Solution

1. Step 1: Review HOC syntax in Vue 3

   A HOC is a function that returns a new component wrapping the original. Using setup and render function with h() is correct.

2. Step 2: Check each option

   const withLogger = (WrappedComponent) => { return { setup() { return () => h(WrappedComponent) } } } returns a component object with setup returning a render function that renders WrappedComponent, which is correct.

3. Final Answer:

   const withLogger = (WrappedComponent) => { return { setup() { return () => h(WrappedComponent) } } } -> Option A

4. Quick Check:

   HOC returns component with setup and render [OK]

Hint: HOCs return a new component wrapping the original with setup [OK]

Common Mistakes:

• Calling setup() directly instead of returning a component
• Using new Vue() in Vue 3 Composition API
• Returning the component function without wrapping

3. Given this HOC code in Vue 3:

const withBorder = (WrappedComponent) => {
  return {
    setup() {
      return () => h('div', { style: { border: '2px solid red' } }, [h(WrappedComponent)])
    }
  }
}

const Base = { template: '
Hello
' }
const Enhanced = withBorder(Base)

What will <Enhanced /> render?

medium

A. Hello

B. Hello

C. Hello

D. Error: h() cannot wrap components

Solution

1. Step 1: Understand the HOC rendering

   The HOC wraps the WrappedComponent inside a div with a red border style.

2. Step 2: Predict the rendered output

   Rendering <Enhanced /> produces a div with red border containing the Base component's paragraph.

3. Final Answer:

   <div style="border: 2px solid red"><p>Hello</p></div> -> Option B

4. Quick Check:

   HOC adds border div around component [OK]

Hint: HOCs wrap output in extra elements or logic [OK]

Common Mistakes:

• Ignoring the wrapping div and expecting only <p>
• Thinking h() cannot wrap components
• Assuming no styles are applied

4. Identify the error in this Vue 3 HOC code:

const withTitle = (WrappedComponent) => {
  return {
    setup() {
      return () => h(WrappedComponent)
    }
  }
}

const Base = { template: '
Hi
' }
const Enhanced = withTitle(Base)

// Usage: <Enhanced title="Welcome" />

What is the problem?

medium

A. The HOC does not pass props to WrappedComponent

B. The HOC should use a class component instead

C. The Base component must be a function, not an object

D. The setup function cannot return a render function

Solution

1. Step 1: Check prop forwarding in HOC

   The HOC returns WrappedComponent but does not forward any props it receives.

2. Step 2: Understand consequence

   When using <Enhanced title="Welcome" />, the title prop is lost because it's not passed down.

3. Final Answer:

   The HOC does not pass props to WrappedComponent -> Option A

4. Quick Check:

   Props must be forwarded in HOCs [OK]

Hint: Always forward props from HOC to wrapped component [OK]

Common Mistakes:

• Forgetting to pass props in render function
• Thinking setup can't return render function
• Believing Base must be a function component

5. You want to create a higher-order component withLoading that shows a loading message while data is loading, then renders the wrapped component with the loaded data. Which approach correctly combines HOC logic with Vue 3 Composition API?

hard

A. Create a mixin that adds loading state and use it inside the wrapped component

B. Modify the wrapped component's template directly to add loading message

C. Use a global variable to track loading and conditionally render wrapped component

D. Return a component with setup() that uses ref for loading state, fetches data, and renders loading or wrapped component with props

Solution

1. Step 1: Understand HOC with loading logic

   The HOC should manage loading state internally and decide what to render based on it.

2. Step 2: Identify correct Vue 3 pattern

   Using setup with ref for loading, fetching data, and returning a render function that shows loading or wrapped component with data is correct.

3. Final Answer:

   Return a component with setup() that uses ref for loading state, fetches data, and renders loading or wrapped component with props -> Option D

4. Quick Check:

   HOC manages state and renders conditionally [OK]

Hint: Use setup with state and conditional render in HOC [OK]

Common Mistakes:

• Changing wrapped component template directly
• Using global variables for state
• Confusing mixins with HOCs