Defining components in Vue - Mini Project: Build & Apply

Defining Components in Vue

📖 Scenario: You are building a simple webpage that shows a greeting message using Vue components. Components help you organize your webpage into small, reusable parts.

🎯 Goal: Create a Vue component named GreetingMessage that displays the text "Hello, Vue learner!" and use it inside the main app.

📋 What You'll Learn

Create a Vue component named GreetingMessage using the <script setup> syntax.

The component should render a <p> tag with the exact text: "Hello, Vue learner!".

Use the GreetingMessage component inside the main App component template.

Use the Composition API with <script setup> and the ref or reactive API if needed.

💡 Why This Matters

🌍 Real World

Vue components let you build webpages by breaking the UI into small, reusable parts. This makes your code easier to manage and reuse.

💼 Career

Knowing how to define and use components is essential for frontend development jobs using Vue.js, a popular framework for building interactive web apps.

1

Create the GreetingMessage component

Create a Vue component named GreetingMessage using <script setup> that renders a <p> tag with the text "Hello, Vue learner!".

Vue

  



// Your script here

Hint

Use the <template> tag to write the HTML and <script setup> for the component script.

2

Set up the main App component

Create the main App component with a <template> and <script setup> tags. Import the GreetingMessage component from the file ./GreetingMessage.vue.

Vue

  



// Import GreetingMessage component here

Hint

Use import GreetingMessage from './GreetingMessage.vue' and include <GreetingMessage /> in the template.

3

Register the GreetingMessage component

In the App component, ensure the GreetingMessage component is properly imported and used inside the <template> section as a self-closing tag.

Vue

  



// Confirm import statement here

Hint

Make sure the component tag is exactly <GreetingMessage /> and the import path is correct.

4

Complete the Vue app setup

Add the export default statement to the App component if needed, or confirm the component is ready to be used as the root component in a Vue app.

Vue

  



import GreetingMessage from './GreetingMessage.vue'
// Your code here

Hint

With <script setup>, you do not need to write export default. Just ensure the component is correctly structured.

Practice

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

easy

A. To handle server-side rendering only

B. To create reusable pieces of UI that can be used throughout the app

C. To connect the app to a database

D. To write CSS styles for the app

Solution

1. Step 1: Understand what components do in Vue

   Components are small, reusable parts of the user interface that can be used multiple times in an app.

2. Step 2: Identify the correct purpose

   Among the options, only creating reusable UI pieces matches the role of components.

3. Final Answer:

   To create reusable pieces of UI that can be used throughout the app -> Option B

4. Quick Check:

   Components = reusable UI blocks [OK]

Hint: Components build reusable UI parts in Vue apps [OK]

Common Mistakes:

• Confusing components with styling or backend logic
• Thinking components handle database connections
• Believing components only work on the server side

2. Which of the following is the correct way to start a Vue component using the Composition API with <script setup>?

easy

A.

{{ message }}

B.

{{ message }}

C.
{{ message }}

D.

{{ message }}

Solution

1. Step 1: Recognize the <script setup> syntax

   In Vue 3, <script setup> is a special syntax that allows direct use of variables without export default.

2. Step 2: Check which option uses <script setup> correctly

   <script setup> const message = 'Hello' </script> <template> <p>{{ message }}</p> </template> declares a variable inside <script setup> and uses it in the template, which is correct.

3. Final Answer:

   <script setup> const message = 'Hello' </script> <template> <p>{{ message }}</p> </template> -> Option A

4. Quick Check:

   <script setup> uses direct variable declaration [OK]

Hint: Use

Common Mistakes:

• Using export default inside
• Declaring variables outside
• Placing <script> after <template> incorrectly

3. Given this Vue component code, what will be displayed when rendered?

<script setup>
import { ref } from 'vue'
const count = ref(0)
function increment() {
  count.value++
}
</script>

<template>
  <button @click="increment">Clicked {{ count }} times</button>
</template>

medium

A. A button showing 'Clicked 0 times' initially, increasing count on each click

B. A button showing 'Clicked 1 times' initially, increasing count on each click

C. A button showing 'Clicked count times' as a literal string

D. An error because count is not reactive

Solution

1. Step 1: Understand ref and reactivity

   The variable count is a reactive reference starting at 0. Using count.value++ updates it reactively.

2. Step 2: Check the template interpolation

   The template uses {{ count }}, which Vue unwraps automatically to show the current value of count.

3. Final Answer:

   A button showing 'Clicked 0 times' initially, increasing count on each click -> Option A

4. Quick Check:

   ref count starts at 0 and updates on click [OK]

Hint: ref variables start at initial value and update reactively [OK]

Common Mistakes:

• Thinking count starts at 1 instead of 0
• Expecting literal 'count' string instead of value
• Assuming count is not reactive without .value

4. Identify the error in this Vue component code:

<script setup>
const props = defineProps({
  title: String
})

function showTitle() {
  console.log(props.title.toUpperCase())
}

showTitle()
</script>

<template>
  <h1>{{ title }}</h1>
</template>

medium

A. Missing import of defineProps

B. Calling showTitle() before props are available

C. Using title in template instead of props.title

D. Using toUpperCase() on a possibly undefined prop

Solution

1. Step 1: Analyze prop definition and usage

   defineProps({ title: String }) declares title without required: true or default value, so props.title can be undefined.

2. Step 2: Locate the error in JS code

   In showTitle(), props.title.toUpperCase() assumes title is a string, but calling toUpperCase() on undefined causes a runtime error.

3. Final Answer:

   Using toUpperCase() on a possibly undefined prop -> Option D

4. Quick Check:

   Validate props before string operations [OK]

Hint: Guard undefined props before methods like toUpperCase [OK]

Common Mistakes:

• Applying string methods to props that may be undefined
• Forgetting to import defineProps (though auto-imported in some setups)
• Assuming props are reactive variables directly

5. You want to create a Vue component that accepts a user prop object with name and age, and displays "Name: [name], Age: [age]". Which is the best way to define and use this prop in a <script setup> component?

hard

A.

Name: {{ user.name }}, Age: {{ user.age }}

B.

Name: {{ props.name }}, Age: {{ props.age }}

C.

Name: {{ props.user.name }}, Age: {{ props.user.age }}

D.

Name: {{ user.name }}, Age: {{ user.age }}

Solution

1. Step 1: Define the prop as an object with expected properties

   The prop user is an object containing name and age, so define it as an Object type and mark required if needed.

2. Step 2: Access the nested properties correctly in the template

   Use props.user.name and props.user.age to display the values inside the template.

3. Final Answer:

   Define user as an object prop and access nested properties via props.user.name and props.user.age -> Option C

4. Quick Check:

   Object prop with nested access = <script setup> const props = defineProps({ user: { type: Object, required: true } }) </script> <template> <p>Name: {{ props.user.name }}, Age: {{ props.user.age }}</p> </template> [OK]

Hint: Define object prop fully and access nested fields via props [OK]

Common Mistakes:

• Defining nested fields as separate props instead of one object
• Destructuring props incorrectly in
• Using defineProps with wrong syntax for objects