Functional components in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a functional component in Vue?

A functional component is a simple Vue component that is stateless and instanceless. It is just a function that returns virtual DOM nodes and does not have its own reactive data or lifecycle hooks.

intermediate

How do you define a functional component in Vue 3?

You define a functional component by creating a function that returns the render output using JSX or the h() function.

beginner

Why might you choose a functional component over a regular component?

Functional components are faster because they do not have reactive state or lifecycle overhead. They are useful for simple UI pieces that only depend on props and do not need internal state or side effects.

beginner

Can functional components in Vue have reactive state or lifecycle hooks?

No, functional components do not have reactive state or lifecycle hooks. They are purely presentational and rely only on props to render their output.

beginner

How do you pass props to a functional component in Vue?

You pass props to a functional component the same way as regular components. The props are received as the first argument in the functional component function.

What is a key characteristic of a Vue functional component?

A It has no reactive state or lifecycle hooks

B It must use class-based syntax

C It always manages its own state

D It cannot receive props

Functional components are stateless and instanceless, so they do not have reactive state or lifecycle hooks.

How do you define a functional component in Vue 3?

A Export a function that returns the render output

B Use the 'data' option to define state

C Use the 'mounted' lifecycle hook

D Define a class component

Functional components are defined by exporting a function that returns the render output.

Which of these is NOT true about Vue functional components?

A They improve performance by skipping lifecycle hooks

B They can have internal reactive state

C They receive props as arguments

D They are useful for simple UI pieces

Functional components do not have internal reactive state.

How do you pass props to a functional component in Vue?

A Props cannot be passed to functional components

B Using the 'data' option

C Using the 'methods' option

D As the first argument to the component function

Props are passed as the first argument to the functional component function.

Which Vue feature is NOT available in functional components?

A Render functions

B Props

C Lifecycle hooks

D Passing slots

Functional components do not have lifecycle hooks.

Explain what a functional component is in Vue and when you might use it.

Think about components that just show data without changing it.

Describe how to create a functional component in Vue 3.

Focus on the function and what it returns.

Practice

1. What is a key characteristic of a functional component in Vue?

easy

A. It manages its own state and lifecycle hooks.

B. It requires a template section to render.

C. It can only be used with class-based components.

D. It is stateless and has no reactive data.

Solution

1. Step 1: Understand functional component basics

   Functional components in Vue are designed to be simple and stateless, meaning they do not hold reactive data or manage lifecycle hooks.

2. Step 2: Compare options with definition

   It is stateless and has no reactive data. correctly states that functional components are stateless. Options A, C, and D describe features not applicable to functional components.

3. Final Answer:

   It is stateless and has no reactive data. -> Option D

4. Quick Check:

   Functional component = stateless [OK]

Hint: Functional components do not hold state or lifecycle hooks [OK]

Common Mistakes:

• Thinking functional components have reactive state
• Assuming they use lifecycle hooks
• Confusing with class-based components

2. Which of the following is the correct syntax to define a functional component using the <script setup> syntax in Vue 3?

easy

A. <script setup functional>\nexport default { props: ['text'] }\n</script>

B. <script setup>\nimport { h } from 'vue'\nconst MyFuncComp = (props) => h('div', props.text)\n</script>

C. <script setup>\nexport default { functional: true, props: ['text'] }\n</script>

D. <script setup>\nconst MyFuncComp = (props) => <div>{props.text}</div>\n</script>

Solution

1. Step 1: Recall Vue 3 functional component syntax

   In Vue 3 with <script setup>, functional components can be defined as functions returning VNodes using the h helper.

2. Step 2: Analyze each option

   <script setup>\nimport { h } from 'vue'\nconst MyFuncComp = (props) => h('div', props.text)\n</script> correctly defines a functional component returning a div with text using h. <script setup>\nconst MyFuncComp = (props) => <div>{props.text}</div>\n</script> uses JSX-like syntax which is not default in Vue. Options B and C use options API syntax incorrectly inside <script setup>.

3. Final Answer:

   <script setup> import { h } from 'vue' const MyFuncComp = (props) => h('div', props.text) </script> -> Option B

4. Quick Check:

   Functional component = function returning VNode with h() [OK]

Hint: Use function returning h() in

Common Mistakes:

• Using options API inside
• Trying to use JSX without setup
• Missing h() helper for rendering

3. Given this functional component code, what will be rendered?

<script setup>
import { h } from 'vue'
const Greeting = (props) => h('p', `Hello, ${props.name}!`)
</script>

<template>
  <Greeting name="Alice" />
</template>

medium

A.

B. Hello, {name}!

C. Hello, Alice!

D. Error: Functional component must return a template

Solution

1. Step 1: Understand the functional component output

   The component Greeting is a function that returns a paragraph element with text including the passed prop name.

2. Step 2: Substitute the prop value

   When used with name="Alice", it renders <p>Hello, Alice!</p> as a normal HTML element.

3. Final Answer:

   <p>Hello, Alice!</p> -> Option C

4. Quick Check:

   Functional component renders HTML with props substituted [OK]

Hint: Functional components return rendered HTML with props values [OK]

Common Mistakes:

• Expecting JSX syntax output
• Thinking it returns raw component tag
• Assuming template is required

4. Identify the error in this functional component code:

<script setup>
const Button = (props) => {
  return <button>{props.label}</button>
}
</script>

medium

A. Using JSX syntax without proper setup causes an error.

B. Missing props declaration in options API.

C. Functional components cannot return elements.

D. The function should not use return statement.

Solution

1. Step 1: Check syntax used in functional component

   The code uses JSX-like syntax (<button>{props.label}</button>) inside a function without JSX support configured.

2. Step 2: Understand Vue default rendering

   Vue requires using h() helper or templates unless JSX is set up. Without JSX setup, this causes a syntax error.

3. Final Answer:

   Using JSX syntax without proper setup causes an error. -> Option A

4. Quick Check:

   JSX needs setup; otherwise use h() or template [OK]

Hint: JSX syntax requires special setup; otherwise use h() [OK]

Common Mistakes:

• Assuming JSX works by default
• Forgetting to import h()
• Thinking return statement is disallowed

5. You want to create a functional component that renders a list of items passed as a prop. Which code correctly implements this in Vue 3 using <script setup> and the h function?

hard

A. <script setup>
import { h } from 'vue'
const ItemList = (props) => h('ul', props.items.map(item => h('li', item)))
</script>

B. <script setup>
const ItemList = { functional: true, props: ['items'], template: '<ul><li v-for="item in items">{{ item }}</li></ul>' }
</script>

C. <script setup>
const ItemList = (props) => {
return <ul>{props.items.map(item => <li>{item}</li>)}

D. <script setup>
import { h } from 'vue'
const ItemList = (props) => h('ul', [h('li', props.items)])
</script>

Solution

1. Step 1: Understand how to render lists in functional components

   Using the h function, you can create an unordered list with list items by mapping over the items array and creating li elements.

2. Step 2: Analyze each option

   <script setup> import { h } from 'vue' const ItemList = (props) => h('ul', props.items.map(item => h('li', item))) </script> correctly maps each item to an li element inside a ul. <script setup> const ItemList = { functional: true, props: ['items'], template: '<ul><li v-for="item in items">{{ item }}</li></ul>' } </script> uses options API incorrectly inside <script setup>. <script setup> const ItemList = (props) => { return <ul>{props.items.map(item => <li>{item}</li>)} uses JSX without setup. <script setup> import { h } from 'vue' const ItemList = (props) => h('ul', [h('li', props.items)]) </script> incorrectly passes the whole array as a single li.

3. Final Answer:

   <script setup> import { h } from 'vue' const ItemList = (props) => h('ul', props.items.map(item => h('li', item))) </script> -> Option A

4. Quick Check:

   Map items to li elements using h() inside ul [OK]

Hint: Map array to h('li', item) inside h('ul') for lists [OK]

Common Mistakes:

• Passing whole array as one li
• Using template syntax inside script setup
• Using JSX without setup