Typing composables in Vue - Performance & Optimization

Performance: Typing composables

LOW IMPACT

Typing composables affects the development experience and bundle size, indirectly influencing load speed and runtime performance.

Defining a composable with and without TypeScript types

Vue

import { ref, Ref } from 'vue';

export function useCounter(): { count: Ref<number>; increment: () => void } {
  const count = ref(0);
  function increment() {
    count.value++;
  }
  return { count, increment };
}

Explicit typing improves code clarity and editor support, reducing bugs and speeding up development.

📈 Performance GainNo runtime cost; improves developer productivity and code maintainability.

Defining a composable with and without TypeScript types

Vue

import { ref } from 'vue';

export function useCounter() {
  const count = ref(0);
  function increment() {
    count.value++;
  }
  return { count, increment };
}

No explicit types can lead to unclear API and potential runtime errors, causing longer debugging and slower development.

📉 Performance CostNo direct runtime cost but increases development time and potential bugs.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Untyped composable	0	0	0	[OK] Good for runtime but risky for dev
Typed composable	0	0	0	[OK] Good for dev experience, no runtime cost

Rendering Pipeline

Typing composables does not affect the browser rendering pipeline directly as it is a compile-time feature.

⚠️ Bottlenecknone

Optimization Tips

1Typing composables improves developer experience without runtime cost.

2TypeScript types are removed during compilation, so they don't affect bundle size or rendering.

3Focus on typing for maintainability, not for runtime performance gains.

Performance Quiz - 3 Questions

How does adding TypeScript types to Vue composables affect runtime performance?

A It increases DOM nodes and reflows.

B It significantly slows down rendering.

C It has no impact on runtime performance.

D It blocks the main thread during user interaction.

DevTools: Network

How to check: Check the bundle size in the Network panel to ensure typing does not add extra runtime code.

What to look for: No increase in bundle size or runtime scripts due to typing annotations.

Practice

1. What is the main purpose of typing composables in Vue with TypeScript?

easy

A. To catch errors early and improve code understanding

B. To make the app run faster

C. To reduce the size of the final bundle

D. To avoid using reactive data

Solution

1. Step 1: Understand typing benefits

   Typing helps catch mistakes before running the code and clarifies what data types are used.

2. Step 2: Compare options

   Only To catch errors early and improve code understanding correctly states the purpose of typing composables; others are unrelated benefits.

3. Final Answer:

   To catch errors early and improve code understanding -> Option A

4. Quick Check:

   Typing composables = catch errors early [OK]

Hint: Typing helps find mistakes before running code [OK]

Common Mistakes:

• Thinking typing improves app speed
• Confusing typing with bundle size reduction
• Believing typing removes reactive data

2. Which of the following is the correct way to type a reactive number in a Vue composable using TypeScript?

easy

A. const count: Ref<number> = ref(0);

B. const count: reactive<number> = reactive(0);

C. const count: number = ref(0);

D. const count: Ref = ref('0');

Solution

1. Step 1: Identify correct typing for reactive refs

   Vue uses Ref<Type> to type reactive refs, so Ref<number> is correct for a number.

2. Step 2: Check each option

   const count: Ref<number> = ref(0); correctly types count as Ref<number>. const count: reactive<number> = reactive(0); uses wrong syntax, C assigns ref to number type, D uses wrong type and string value.

3. Final Answer:

   const count: Ref<number> = ref(0); -> Option A

4. Quick Check:

   Use Ref<Type> for reactive refs [OK]

Hint: Use Ref<Type> to type reactive refs in composables [OK]

Common Mistakes:

• Using reactive instead of Ref for refs
• Assigning ref() to plain types
• Mismatching value type and Ref generic

3. Given this composable code, what is the type of message inside the component?

import { ref } from 'vue';

export function useMessage() {
  const message = ref('Hello');
  return { message };
}

medium

A. string

B. Ref<string>

C. Ref<any>

D. any

Solution

1. Step 1: Understand ref return type

   The ref function returns a Ref object wrapping the value type, here a string.

2. Step 2: Determine message type

   Since message is created by ref('Hello'), its type is Ref<string>.

3. Final Answer:

   Ref<string> -> Option B

4. Quick Check:

   ref('text') returns Ref<string> [OK]

Hint: ref('text') returns Ref<string> type [OK]

Common Mistakes:

• Assuming message is plain string
• Using Ref<any> without specifying type
• Confusing Ref<string> with string

4. Identify the error in this typed composable code:

import { ref, Ref } from 'vue';

export function useCounter(): { count: Ref<number> } {
  const count = ref('0');
  return { count };
}

medium

A. Ref type is not imported

B. Return type is missing

C. count should be reactive, not ref

D. ref is called with a string instead of a number

Solution

1. Step 1: Check ref argument type

   The function expects count to be Ref<number>, but ref is called with a string '0'.

2. Step 2: Identify mismatch error

   This causes a type mismatch error because the initial value type does not match the declared Ref generic.

3. Final Answer:

   ref is called with a string instead of a number -> Option D

4. Quick Check:

   ref argument type must match Ref generic [OK]

Hint: Check ref initial value matches declared Ref type [OK]

Common Mistakes:

• Passing wrong type to ref()
• Ignoring return type mismatch
• Confusing reactive and ref usage

5. How would you correctly type a composable that returns a reactive object with a string title and a number count using Vue's Ref type?

import { ref, Ref } from 'vue';

export function useData() {
  const title = ref('My Title');
  const count = ref(10);
  return { title, count };
}

hard

A. export function useData(): { title: reactive<string>; count: reactive<number> }

B. export function useData(): { title: string; count: number }

C. export function useData(): { title: Ref<string>; count: Ref<number> }

D. export function useData(): { title: Ref<any>; count: Ref<any> }

Solution

1. Step 1: Identify types of returned refs

   Both title and count are refs holding string and number respectively, so their types are Ref<string> and Ref<number>.

2. Step 2: Match return type signature

   The function return type should reflect these as an object with keys typed as Ref<string> and Ref<number>.

3. Final Answer:

   export function useData(): { title: Ref<string>; count: Ref<number> } -> Option C

4. Quick Check:

   Return type matches Ref types of reactive data [OK]

Hint: Return type must match Ref types of reactive variables [OK]

Common Mistakes:

• Typing return values as plain string or number
• Using Ref<any> instead of specific types
• Using reactive instead of Ref in type