Why TypeScript matters in Vue - See It in Action

Why TypeScript matters in Vue

📖 Scenario: You are building a small Vue app to display user profiles. You want to make sure your code is clear and safe from common mistakes.

🎯 Goal: Create a Vue component using TypeScript to define user data and display it safely.

📋 What You'll Learn

Create a reactive user object with exact properties

Add a TypeScript interface for the user data

Use the interface to type the reactive user object

Display the user name and age in the template

💡 Why This Matters

🌍 Real World

Using TypeScript in Vue helps catch errors early and makes your code easier to understand and maintain, especially in bigger projects.

💼 Career

Many companies use TypeScript with Vue to build reliable web apps. Knowing how to combine them is a valuable skill for frontend developers.

1

Set up user data with TypeScript interface

Create a TypeScript interface called User with properties name as string and age as number.

Vue

// Your code here

Hint

Use interface User { name: string; age: number; } to define the user shape.

2

Create reactive user object with type

Create a reactive variable called user of type User with name set to 'Alice' and age set to 30 using Vue's ref or reactive.

Vue

interface User {
  name: string;
  age: number;
}

// Your code here

Hint

Use const user = reactive<User>({ name: 'Alice', age: 30 }) to create typed reactive data.

3

Add template to display user data

Add a Vue template that displays the user's name inside an <h1> and the age inside a <p>.

Vue

import { reactive } from 'vue';

interface User {
  name: string;
  age: number;
}

const user = reactive({
  name: 'Alice',
  age: 30
});

// Your code here

Hint

Use <h1>{{ user.name }}</h1> and <p>{{ user.age }}</p> inside the template.

4

Complete component with accessibility and typing

Add aria-label="User Profile" to the <h1> tag and ensure the script uses lang="ts" for TypeScript support.

Vue

  {{ user.name }}
  {{ user.age }}



import { reactive } from 'vue';

interface User {
  name: string;
  age: number;
}

const user = reactive({
  name: 'Alice',
  age: 30
});

Hint

Add aria-label="User Profile" to the <h1> for accessibility and confirm lang="ts" is in the script tag.

Practice

1. Why is using TypeScript beneficial when developing Vue applications?

easy

A. It automatically writes all the code for you.

B. It makes the app run faster in the browser.

C. It removes the need for Vue components.

D. It helps catch errors before running the app.

Solution

1. Step 1: Understand TypeScript's role in development

   TypeScript checks your code for mistakes before you run it, helping avoid bugs early.

2. Step 2: Compare benefits with other options

   Options B, C, and D are incorrect because TypeScript does not speed up runtime, remove components, or auto-generate code.

3. Final Answer:

   It helps catch errors before running the app. -> Option D

4. Quick Check:

   TypeScript catches errors early [OK]

Hint: TypeScript finds mistakes before running code [OK]

Common Mistakes:

• Thinking TypeScript speeds up app runtime
• Believing TypeScript replaces Vue components
• Assuming TypeScript writes code automatically

2. Which of the following is the correct way to declare a typed prop in a Vue component using TypeScript?

easy

A. const props = defineProps<{ name: string }>()

B. props: { name: { type: String, required: true } }

C. props: { name: String }

D. props: { name: any }

Solution

1. Step 1: Identify TypeScript syntax for props in Vue 3

   Using const props = defineProps<{ name: string }>() is the correct TypeScript way to type props in Vue 3's Composition API.

2. Step 2: Check other options for correctness

   Options A and B use JavaScript style without TypeScript typing. props: { name: any } uses any, which loses type safety.

3. Final Answer:

   const props = defineProps<{ name: string }>() -> Option A

4. Quick Check:

   Typed props in Vue 3 use defineProps with TypeScript [OK]

Hint: Use defineProps with TypeScript type for props [OK]

Common Mistakes:

• Using JavaScript prop syntax without types
• Using 'any' type which disables type checking
• Confusing Vue 2 and Vue 3 prop declarations

3. Given this Vue component code using TypeScript:

const count = ref(0);
function increment() {
  count.value += 1;
}
increment();
console.log(count.value);

What will be logged to the console?

medium

A. 1

B. 0

C. undefined

D. Error: count is not defined

Solution

1. Step 1: Understand ref and value in Vue with TypeScript

   ref(0) creates a reactive number starting at 0. Access with count.value.

2. Step 2: Trace the increment function and console log

   Calling increment() adds 1 to count.value, so it becomes 1. Then logging count.value outputs 1.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Increment ref value once [OK]

Hint: Remember to access ref values with .value [OK]

Common Mistakes:

• Logging ref variable without .value
• Assuming ref is a plain number
• Forgetting to call increment before logging

4. What is the main issue with this Vue + TypeScript code snippet?

const message = ref('Hello');
message = 'Hi';

medium

A. The ref function is missing an import statement.

B. You cannot assign a string directly to a ref variable.

C. The string 'Hi' should be wrapped in ref().

D. The variable message should be declared with let instead of const.

Solution

1. Step 1: Understand ref assignment rules in Vue with TypeScript

   A ref variable holds an object with a .value property. You cannot assign a string directly to the ref variable itself.

2. Step 2: Identify correct way to update ref value

   To change the string inside the ref, assign to message.value = 'Hi', not message = 'Hi'.

3. Final Answer:

   You cannot assign a string directly to a ref variable. -> Option B

4. Quick Check:

   Ref variables require .value for assignment [OK]

Hint: Assign to .value, not the ref variable itself [OK]

Common Mistakes:

• Assigning directly to ref variable instead of .value
• Confusing ref with normal variables
• Ignoring TypeScript error messages

5. You want to create a Vue component with a prop that accepts either a string or number, and you want TypeScript to enforce this. Which is the best way to declare this prop using Vue 3 and TypeScript?

hard

A. props: defineProps<{ value: any }>()

B. props: { value: [String, Number] }

C. const props = defineProps<{ value: string | number }>()

D. props: { value: { type: [String, Number], required: true } }

Solution

1. Step 1: Use TypeScript union types in defineProps

   Using const props = defineProps<{ value: string | number }>() tells TypeScript the prop can be string or number, enforcing type safety.

2. Step 2: Compare with other options

   Options B and C use JavaScript style without TypeScript type checking. props: defineProps<{ value: any }>() uses any, which disables type safety.

3. Final Answer:

   const props = defineProps<{ value: string | number }>() -> Option C

4. Quick Check:

   Use TypeScript union types with defineProps [OK]

Hint: Use TypeScript union types in defineProps for multiple types [OK]

Common Mistakes:

• Using JavaScript prop arrays without TypeScript types
• Using any type which disables checks
• Not using defineProps in Vue 3 Composition API