h function for creating vnodes in Vue - Mini Project: Build & Apply

Using the h Function to Create VNodes in Vue

📖 Scenario: You are building a simple Vue 3 component that displays a greeting message using the h function to create virtual nodes (vnodes).

🎯 Goal: Build a Vue 3 component using the h function to create a <div> element containing a <h1> heading with the text "Hello, Vue!".

📋 What You'll Learn

Create a Vue 3 component using `defineComponent`.

Use the h function from Vue to create virtual nodes.

Render a <div> element as the root with an <h1> child containing the text "Hello, Vue!".

Do not use template syntax; use only the h function for rendering.

💡 Why This Matters

🌍 Real World

Using the h function is useful when you want to create Vue components programmatically without templates, such as in render functions or JSX alternatives.

💼 Career

Understanding how to create virtual nodes with the h function helps you build flexible Vue components and is a key skill for advanced Vue development and custom render logic.

1

Setup Vue Component and Import h

Create a Vue 3 component by importing defineComponent and h from 'vue'. Then define a component named HelloVue using defineComponent.

Vue

import { defineComponent, h } from 'vue'

// Your code here

Hint

Start by importing defineComponent and h from 'vue'. Then create a component with defineComponent and give it the name HelloVue.

2

Add a Render Function Using h

Inside the HelloVue component, add a render function that returns a virtual node created by h. For now, return a <div> element with no children.

Vue

import { defineComponent, h } from 'vue'

export default defineComponent({
  name: 'HelloVue',
  render() {
    // Your code here
  }
})

Hint

Define a render method that returns h('div') to create an empty <div> element.

3

Add an <h1> Child with Text

Modify the render function to return a <div> element with one child: an <h1> element containing the text "Hello, Vue!". Use h to create both elements and nest the <h1> inside the <div>.

Vue

import { defineComponent, h } from 'vue'

export default defineComponent({
  name: 'HelloVue',
  render() {
    // Your code here
  }
})

Hint

Use h('div', [h('h1', 'Hello, Vue!')]) to create a <div> with an <h1> child containing the text.

4

Export the Component as Default

Ensure the HelloVue component is exported as the default export so it can be used in a Vue app.

Vue

import { defineComponent, h } from 'vue'

// Your code here

Hint

Make sure the component is exported with export default defineComponent.

Practice

1. What is the primary purpose of the h function in Vue?

easy

A. To define CSS styles for components

B. To directly manipulate the DOM elements

C. To fetch data from an API

D. To create virtual nodes representing elements or components

Solution

1. Step 1: Understand the role of h in Vue

   The h function is used to create virtual nodes (vnodes) which represent elements or components in Vue's virtual DOM.

2. Step 2: Differentiate from other functions

   It does not manipulate the real DOM directly, fetch data, or style components. Its main role is to build the virtual DOM structure.

3. Final Answer:

   To create virtual nodes representing elements or components -> Option D

4. Quick Check:

   h function = create virtual nodes [OK]

Hint: Remember: h builds virtual nodes, not real DOM [OK]

Common Mistakes:

• Confusing h with direct DOM manipulation
• Thinking h fetches data
• Assuming h styles components

2. Which of the following is the correct syntax to create a div element with the h function and a class of "container"?

easy

A. h('div', ['class', 'container'])

B. h('div', { class: 'container' })

C. h('div', 'class', 'container')

D. h('div', { 'className': 'container' })

Solution

1. Step 1: Recall the h function signature

   The h function takes the tag name as the first argument and an object of props as the second argument.

2. Step 2: Identify correct props syntax

   Vue uses class (not className) as the key for CSS classes in the props object.

3. Final Answer:

   h('div', { class: 'container' }) -> Option B

4. Quick Check:

   h(tag, props) with class key = A [OK]

Hint: Props are an object; use { class: 'name' } [OK]

Common Mistakes:

• Using 'className' instead of 'class'
• Passing class as separate string arguments
• Using array instead of object for props

3. What will be the rendered output of this Vue render function snippet?

return h('ul', null, [
  h('li', null, 'Apple'),
  h('li', null, 'Banana'),
  h('li', null, 'Cherry')
])

medium

A. AppleBananaCherry

B. AppleBananaCherry

C. AppleBananaCherry

D. Error: Children must be strings

Solution

1. Step 1: Understand the structure created by h

   The outer h creates a ul element with an array of li children nodes.

2. Step 2: Recognize the children rendering

   Each li vnode contains a string child representing the fruit name, so the final HTML is a list with three li items.

3. Final Answer:

   <ul><li>Apple</li><li>Banana</li><li>Cherry</li></ul> -> Option A

4. Quick Check:

   h with array children = nested elements [OK]

Hint: Array children create nested elements inside parent [OK]

Common Mistakes:

• Thinking children array concatenates text
• Expecting error for array children
• Missing the parent <ul> element

4. Identify the error in this usage of the h function:

return h('button', { onclick: () => alert('Clicked!') }, 'Click me')

medium

A. The event name should be lowercase: 'onclick'

B. The event handler should be passed as 'onClick' but as a string

C. The event handler should be passed as 'onClick' with capital C

D. The event handler should be passed as 'onClick' but inside an array

Solution

1. Step 1: Recall Vue event listener naming in h

   Vue expects event listeners in props to be prefixed with 'on' and camelCase event name, e.g., 'onClick'.

2. Step 2: Identify the incorrect casing

   The code uses 'onclick' with lowercase 'c', which Vue does not recognize as an event listener.

3. Final Answer:

   The event handler should be passed as 'onClick' with capital C -> Option C

4. Quick Check:

   Event props use camelCase event names [OK]

Hint: Use camelCase event names like 'onClick' in props [OK]

Common Mistakes:

• Using lowercase event names
• Passing event handler as string
• Wrapping handler in array unnecessarily

5. How would you use the h function to create a ul list from this array of fruits, but only include fruits with names longer than 5 characters?

const fruits = ['Apple', 'Banana', 'Fig', 'Cherry']

hard

A. h('ul', null, fruits.filter(f => f.length > 5).map(f => h('li', null, f)))

B. h('ul', null, fruits.map(f => f.length > 5 ? h('li', null, f) : f))

C. h('ul', null, fruits.map(f => h('li', null, f.length > 5)))

D. h('ul', null, fruits.filter(f => f.length > 5))

Solution

1. Step 1: Filter fruits by length

   Use filter to keep only fruits with names longer than 5 characters.

2. Step 2: Map filtered fruits to li vnodes

   Use map to convert each filtered fruit into an li vnode with the fruit name as child.

3. Step 3: Pass the array of li vnodes as children to ul

   This creates a ul with only the desired fruits as list items.

4. Final Answer:

   h('ul', null, fruits.filter(f => f.length > 5).map(f => h('li', null, f))) -> Option A

5. Quick Check:

   Filter then map to
6. nodes = A [OK]

Hint: Filter first, then map to <li> nodes inside h [OK]

Common Mistakes:

• Mapping without filtering includes unwanted items
• Passing booleans or nulls as children
• Passing raw strings array without wrapping in <li>