Loading states pattern in Vue - Mini Project: Build & Apply

Loading States Pattern in Vue

📖 Scenario: You are building a simple Vue app that fetches user data from an API. To improve user experience, you want to show a loading message while the data is being fetched.

🎯 Goal: Create a Vue component that shows a loading message while fetching data and then displays the user name once loaded.

📋 What You'll Learn

Use Vue 3 Composition API with <script setup>

Create a reactive loading signal to track loading state

Create a reactive user object to hold fetched data

Simulate data fetching with setTimeout

Show Loading... text while loading is true

Show user name after loading is false

💡 Why This Matters

🌍 Real World

Loading states are common in web apps to inform users that data is being fetched or processed, preventing confusion or frustration.

💼 Career

Understanding loading states and reactive UI updates is essential for frontend developers building responsive and user-friendly applications.

1

Setup reactive user data

Create a Vue component with <script setup> and define a reactive variable called user initialized to an empty object {}.

Vue

// Define reactive user object
// Your code here



  

Hint

Use reactive from Vue to create a reactive object called user.

2

Add loading state variable

Add a reactive boolean variable called loading initialized to true inside the <script setup> section.

Vue

import { reactive, ref } from 'vue'

const user = reactive({})
// Define loading state variable
// Your code here



  

Hint

Use ref from Vue to create a boolean loading variable set to true.

3

Simulate data fetching and update states

Inside <script setup>, use setTimeout to simulate fetching data after 2 seconds. Inside the timeout callback, set user.name to 'Alice' and set loading.value to false.

Vue

import { reactive, ref } from 'vue'

const user = reactive({})
const loading = ref(true)

// Simulate data fetching
// Your code here



  

Hint

Use setTimeout to delay 2 seconds, then update user.name and loading.value.

4

Add template to show loading and user name

Add a <template> section that shows Loading... text when loading.value is true, and shows User: {{ user.name }} when loading.value is false.

Vue

import { reactive, ref } from 'vue'

const user = reactive({})
const loading = ref(true)

setTimeout(() => {
  user.name = 'Alice'
  loading.value = false
}, 2000)



  
  

Hint

Use v-if to show loading text and v-else to show user name.

Practice

1. What is the main purpose of using a loading state in a Vue component?

easy

A. To disable Vue reactivity

B. To show users that data is being fetched or processed

C. To permanently hide content from users

D. To increase the component's size

Solution

1. Step 1: Understand user experience during data fetching

   Loading states inform users that the app is working on a task, preventing confusion.

2. Step 2: Identify the purpose of loading states in Vue

   They show progress or waiting messages while data loads or actions complete.

3. Final Answer:

   To show users that data is being fetched or processed -> Option B

4. Quick Check:

   Loading states = user feedback [OK]

Hint: Loading states show progress to users during waits [OK]

Common Mistakes:

• Thinking loading states hide content permanently
• Confusing loading states with disabling reactivity
• Assuming loading states change component size

2. Which Vue syntax correctly shows a loading message only when isLoading is true?

easy

A. <div v-show="isLoading">Loading...</div>

B. <div v-if="!isLoading">Loading...</div>

C. <div v-if="isLoading">Loading...</div>

D. <div v-bind:isLoading>Loading...</div>

Solution

1. Step 1: Understand v-if usage

   v-if conditionally renders the element only if the expression is true.

2. Step 2: Match condition to show loading

   We want to show the message when isLoading is true, so v-if="isLoading" is correct.

3. Final Answer:

   <div v-if="isLoading">Loading...</div> -> Option C

4. Quick Check:

   Show loading if isLoading true = v-if="isLoading" [OK]

Hint: Use v-if with the loading variable directly [OK]

Common Mistakes:

• Using v-if with negation (!isLoading) to show loading
• Using v-show which toggles visibility but keeps element
• Using invalid v-bind syntax for conditional rendering

3. Given this Vue setup:

const isLoading = ref(true);
setTimeout(() => { isLoading.value = false; }, 2000);

What will the component show initially if template has <div v-if="isLoading">Loading...</div><div v-else>Content Loaded</div>?

medium

A. Loading... for 2 seconds, then Content Loaded

B. Content Loaded immediately

C. Nothing is shown

D. Loading... forever

Solution

1. Step 1: Analyze initial value of isLoading

   It starts as true, so v-if="isLoading" shows "Loading..." initially.

2. Step 2: Understand the timeout effect

   After 2 seconds, isLoading.value becomes false, switching to v-else content "Content Loaded".

3. Final Answer:

   Loading... for 2 seconds, then Content Loaded -> Option A

4. Quick Check:

   Initial true shows loading, then false shows content [OK]

Hint: Check initial state and delayed change for output [OK]

Common Mistakes:

• Assuming content shows immediately ignoring initial true
• Thinking loading never stops without reactivity knowledge
• Confusing v-if and v-else rendering timing

4. Identify the error in this Vue code snippet for loading state:

const isLoading = ref(false);

function fetchData() {
  isLoading = true;
  fetch('/api/data')
    .then(() => { isLoading = false; });
}

medium

A. No error, code works fine

B. Missing async keyword on fetchData function

C. fetch API call is incorrect syntax

D. Directly assigning to ref variable instead of its .value

Solution

1. Step 1: Understand how to update Vue refs

   Refs are objects; their value must be changed via .value, not by direct assignment.

2. Step 2: Identify incorrect assignments

   Code assigns isLoading = true instead of isLoading.value = true, causing errors.

3. Final Answer:

   Directly assigning to ref variable instead of its .value -> Option D

4. Quick Check:

   Update ref with .value, not direct assignment [OK]

Hint: Change ref values with .value property [OK]

Common Mistakes:

• Assigning ref variable directly instead of .value
• Forgetting to handle promise with then or async/await
• Assuming fetch syntax is wrong when it is correct

5. You want to disable a submit button during loading in Vue. Which code snippet correctly disables the button and shows loading text using isLoading reactive variable?

hard

A. <button :disabled="isLoading">{{ isLoading ? 'Loading...' : 'Submit' }}</button>

B. <button v-if="isLoading" disabled>Submit</button><button v-else>Loading...</button>

C. <button :disabled="!isLoading">Submit</button>

D. <button :loading="isLoading">Submit</button>

Solution

1. Step 1: Disable button based on loading state

   Use :disabled="isLoading" to disable the button when loading.

2. Step 2: Show dynamic button text

   Use interpolation with a ternary to show "Loading..." or "Submit" based on isLoading.

3. Final Answer:

   <button :disabled="isLoading">{{ isLoading ? 'Loading...' : 'Submit' }}</button> -> Option A

4. Quick Check:

   Disable button and show loading text with :disabled and ternary [OK]

Hint: Bind :disabled and use ternary text inside button [OK]

Common Mistakes:

• Using v-if to swap buttons instead of disabling
• Negating isLoading for disabling logic
• Using non-existent :loading attribute on button