Setting up TypeScript in Vue project - Practice Exercises

Challenge - 5 Problems

📝 Syntax

intermediate

Correct TypeScript setup in Vue component

Which option shows the correct way to declare a Vue 3 component using TypeScript with the Composition API?

Vue

<script setup lang="ts">
import { ref } from 'vue'

const count = ref(0)
function increment() {
  count.value++
}
</script>

<template>
  <button @click="increment">Count is: {{ count }}</button>
</template>

A

<script lang="ts">
import { ref } from 'vue'
const count = ref(0)
function increment() {
  count++
}
</script>

B

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

C

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

D

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

💡 Hint

Remember to specify lang="ts" and use .value to update refs.

Option B correctly uses lang="ts" in the <script setup> block, declares count as a ref<number>, and increments count.value. This follows Vue 3 Composition API with TypeScript.

Option B misses setup and incorrectly increments count directly.

Option B misses lang="ts", so TypeScript is not enabled.

Option B sets count as a string ref, causing a type mismatch when incrementing.

❓ component_behavior

intermediate

TypeScript prop typing in Vue component

Given this Vue component using TypeScript, what is the type of the prop title inside the component?

Vue

<script setup lang="ts">
import { defineProps } from 'vue'

const props = defineProps<{ title: string }>()
</script>

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

A string

B any

C number

D undefined

💡 Hint

Check the type declared inside defineProps.

The defineProps<{ title: string }>() declares title as a string prop. So inside the component, title is typed as string.

🔧 Debug

advanced

Identify the TypeScript error in Vue component

What TypeScript error will this Vue component produce?

Vue

<script setup lang="ts">
import { ref } from 'vue'

const count = ref(0)
function increment() {
  count++
}
</script>

A TS2363: The operand of an increment or decrement operator must be a variable, property or indexer.

B TS2362: The left-hand side of an assignment expression must be a variable or a property access.

C TypeError: count is not a number

D TS2339: Property 'value' does not exist on type 'number'.

💡 Hint

Remember how to update a ref value in Vue with TypeScript.

The variable count is a ref object, so you must increment count.value, not count directly. Incrementing count++ causes error TS2363 because count is not a variable holding a number but a ref object.

🧠 Conceptual

advanced

Why use lang="ts" in Vue <script>?

What is the main purpose of adding lang="ts" attribute to the <script> tag in a Vue component?

A It makes the component compatible only with Vue 2 projects.

B It automatically converts JavaScript code to TypeScript at runtime.

C It disables JavaScript and only allows TypeScript syntax.

D It enables TypeScript support and type checking inside the script block.

💡 Hint

Think about what TypeScript does during development.

Adding lang="ts" tells the Vue build system to treat the script block as TypeScript, enabling type checking and TS features during development and build time.

It does not convert JS to TS at runtime (B), nor disables JS entirely (C), nor restricts Vue version (D).

❓ state_output

expert

Output of Vue component with TypeScript reactive state

What will be the rendered output after clicking the button twice in this Vue component?

Vue

<script setup lang="ts">
import { reactive } from 'vue'

const state = reactive({ count: 0 })
function increment() {
  state.count++
}
</script>

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

A Clicked NaN times

B Clicked 0 times

C Clicked 2 times

D Clicked undefined times

💡 Hint

Check how reactive state updates and reflects in template.

The reactive object state has a count property initialized to 0. Each click increments state.count by 1. After two clicks, state.count is 2, so the button text shows "Clicked 2 times".

Practice

1. What is the main benefit of using TypeScript in a Vue project?

easy

A. It helps catch errors early and improves code clarity.

B. It automatically styles your components.

C. It replaces Vue's template syntax with HTML.

D. It removes the need for JavaScript entirely.

Solution

1. Step 1: Understand TypeScript's role

   TypeScript adds static typing to JavaScript, helping catch errors before running code.

2. Step 2: Relate to Vue projects

   Using TypeScript in Vue improves code clarity and reduces runtime bugs.

3. Final Answer:

   It helps catch errors early and improves code clarity. -> Option A

4. Quick Check:

   TypeScript improves code safety = A [OK]

Hint: TypeScript catches errors before running code [OK]

Common Mistakes:

• Thinking TypeScript styles components
• Confusing TypeScript with HTML templates
• Believing TypeScript removes JavaScript

2. Which command is used to create a new Vue project with TypeScript support?

easy

A. vue create project --typescript

B. npm create vue@latest and select TypeScript option

C. npm install vue typescript

D. vue add typescript

Solution

1. Step 1: Identify the official Vue CLI command

   The recommended way is using npm create vue@latest to start a new project.

2. Step 2: Select TypeScript during setup

   During the interactive setup, you choose TypeScript to enable it.

3. Final Answer:

   npm create vue@latest and select TypeScript option -> Option B

4. Quick Check:

   Use npm create vue@latest for new Vue projects [OK]

Hint: Use npm create vue@latest and pick TypeScript [OK]

Common Mistakes:

• Using old vue CLI commands
• Trying to install TypeScript separately after project creation
• Confusing add commands with create commands

3. Given this Vue component script tag, what is missing to enable TypeScript?

<script>
export default {
  data() {
    return { count: 0 }
  }
}
</script>

medium

A. Wrap the export in a defineComponent call

B. Change data() to setup()

C. Add type="module" to the <script> tag

D. Add lang="ts" attribute to the <script> tag

Solution

1. Step 1: Identify how to enable TypeScript in Vue scripts

   Vue requires lang="ts" on the <script> tag to treat it as TypeScript.

2. Step 2: Check other options

   Changing to setup() or adding type="module" does not enable TypeScript automatically.

3. Final Answer:

   Add lang="ts" attribute to the <script> tag -> Option D

4. Quick Check:

   Use lang="ts" to enable TypeScript [OK]

Hint: Add lang="ts" to script tag for TypeScript [OK]

Common Mistakes:

• Forgetting lang="ts" on script tag
• Confusing setup() with TypeScript enabling
• Assuming type="module" enables TypeScript

4. You added lang="ts" to your Vue component but get errors about missing types. What is the likely cause?

medium

A. You forgot to create or configure tsconfig.json in the project root.

B. You need to remove lang="ts" to fix errors.

C. Vue does not support TypeScript in single file components.

D. You must rename the file extension to .ts instead of .vue.

Solution

1. Step 1: Understand TypeScript configuration needs

   TypeScript requires a tsconfig.json file to know how to compile and check types.

2. Step 2: Check other options

   Removing lang="ts" disables TypeScript, Vue supports TypeScript in .vue files, and renaming files is not needed.

3. Final Answer:

   You forgot to create or configure tsconfig.json in the project root. -> Option A

4. Quick Check:

   tsconfig.json is required for TypeScript setup [OK]

Hint: Create tsconfig.json to avoid missing type errors [OK]

Common Mistakes:

• Removing lang="ts" instead of fixing config
• Thinking Vue disallows TypeScript in .vue files
• Renaming .vue files to .ts incorrectly

5. You want to use TypeScript in a Vue 3 project with the Composition API. Which setup is correct for the script block?

hard

A. <script lang="js" setup>
import { ref } from 'vue'
const count = ref(0)
</script>

B. <script>
import { ref } from 'vue'
const count = ref(0)
</script>

C. <script lang="ts" setup>
import { ref } from 'vue'
const count = ref(0)
</script>

D. <script lang="ts">
export default {
data() { return { count: 0 } }
}
</script>

Solution

1. Step 1: Identify TypeScript and Composition API usage

   Using lang="ts" setup enables TypeScript and Composition API syntax in Vue 3.

2. Step 2: Check other options

   The version with lang="js" setup uses JavaScript not TypeScript, the plain <script> lacks the lang="ts" attribute, and the one using export default with data() is Options API, not Composition API.

3. Final Answer:

   <script lang="ts" setup> with ref import and usage -> Option C

4. Quick Check:

   Use lang="ts" setup for Composition API with TypeScript [OK]

Hint: Use

Common Mistakes:

• Omitting lang="ts" for TypeScript
• Using lang="js" instead of lang="ts"
• Mixing Options API with Composition API syntax