Why dApps need user interfaces in Blockchain / Solidity - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to display a simple message in a dApp UI.

Blockchain / Solidity

console.log([1]);

Drag options to blanks, or click blank then click option'

A"Welcome to the dApp!"

BWelcome to the dApp!

Cconsole.log

Dalert

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the message text.

The message must be a string inside quotes to display correctly in console.log.

2fill in blank

medium

Complete the code to create a button element in HTML for a dApp UI.

Blockchain / Solidity

<button>[1]</button>

Drag options to blanks, or click blank then click option'

Asubmit

B<button>

Cdiv

DClick me

Attempts:

3 left

💡 Hint

Common Mistakes

Putting HTML tags inside the button instead of text.

The button text should be inside the button tags as plain text.

3fill in blank

hard

Fix the error in the JavaScript code that updates a dApp UI element.

Blockchain / Solidity

document.getElementById('status').[1] = 'Connected';

Drag options to blanks, or click blank then click option'

AinnerHTML

Bvalue

Cconsole

DgetElementById

Attempts:

3 left

💡 Hint

Common Mistakes

Using value instead of innerHTML for div or span elements.

To change the visible text inside an HTML element, use innerHTML property.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps words to their lengths only if length is greater than 3.

Blockchain / Solidity

{word: [1] for word in words if [2] > 3}

Drag options to blanks, or click blank then click option'

Alen(word)

Bword

Dword.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using word instead of len(word) for length.

Use len(word) to get the length of each word for both the value and the condition.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase keys to values only if value is positive.

Blockchain / Solidity

result = [1]: [2] for k, v in data.items() if [3] > 0

Drag options to blanks, or click blank then click option'

Ak.upper()

Bv

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using k instead of k.upper() for keys.

Checking k instead of v in condition.

Use k.upper() for uppercase keys, v for values, and check if v > 0.

Practice

1. Why do decentralized applications (dApps) need user interfaces?

easy

A. To allow users to interact with blockchain features easily

B. To increase the blockchain transaction speed

C. To store data on the blockchain

D. To mine new cryptocurrency coins

Solution

1. Step 1: Understand the role of user interfaces in dApps

   User interfaces help users interact with complex blockchain features without needing technical knowledge.

2. Step 2: Identify the main purpose of user interfaces

   User interfaces make dApps accessible and easy to use for everyone.

3. Final Answer:

   To allow users to interact with blockchain features easily -> Option A

4. Quick Check:

   User interfaces = easy interaction [OK]

Hint: User interfaces make blockchain apps easy for people [OK]

Common Mistakes:

• Confusing user interface with blockchain speed
• Thinking UI stores blockchain data
• Mixing UI with mining functions

2. Which of the following is the correct way to describe a user interface for a dApp?

easy

A. A command-line tool that requires coding knowledge

B. A blockchain node software

C. A graphical interface that simplifies user interaction

D. A cryptocurrency wallet without UI

Solution

1. Step 1: Define what a user interface is

   A user interface is a graphical or visual tool that helps users interact with software easily.

2. Step 2: Match the description to dApp UI

   A dApp UI should simplify interaction, so a graphical interface fits best.

3. Final Answer:

   A graphical interface that simplifies user interaction -> Option C

4. Quick Check:

   UI = graphical and simple [OK]

Hint: UI means graphical and easy to use, not command-line [OK]

Common Mistakes:

• Confusing UI with backend software
• Thinking UI must be command-line
• Ignoring the need for simplicity

3. Consider this simple dApp UI code snippet in JavaScript:

const button = document.createElement('button');
button.textContent = 'Send Transaction';
button.onclick = () => alert('Transaction sent!');
document.body.appendChild(button);

What happens when the user clicks the button?

medium

A. An alert box shows 'Transaction sent!'

B. The page reloads

C. A blockchain transaction is automatically sent

D. Nothing happens

Solution

1. Step 1: Analyze the button creation and event

   The code creates a button labeled 'Send Transaction' and sets an onclick event to show an alert.

2. Step 2: Understand the onclick event behavior

   When clicked, the alert with message 'Transaction sent!' appears; no actual blockchain call is made.

3. Final Answer:

   An alert box shows 'Transaction sent!' -> Option A

4. Quick Check:

   Button click triggers alert [OK]

Hint: onclick triggers alert, not real transaction [OK]

Common Mistakes:

• Assuming blockchain transaction happens automatically
• Thinking page reloads on click
• Ignoring the alert function

4. This dApp UI code has an error:

const btn = document.createElement('button')
btn.textContent = 'Connect Wallet'
btn.onclick = () => console.log('Wallet connected')
document.body.appendChild(btn)

What is the error and how to fix it?

medium

A. Missing semicolons cause syntax error; add semicolons

B. onclick function syntax is wrong; use function keyword

C. Button is not added to the page; fix appendChild argument

D. No error; code works fine

Solution

1. Step 1: Check JavaScript syntax

   JavaScript allows omitting semicolons; the code syntax is valid.

2. Step 2: Verify button creation and event

   The button is created, text set, onclick logs message, and appended correctly.

3. Final Answer:

   No error; code works fine -> Option D

4. Quick Check:

   Code syntax is valid and functional [OK]

Hint: JS allows no semicolons; check logic not punctuation [OK]

Common Mistakes:

• Thinking missing semicolons cause error
• Assuming appendChild needs different argument
• Confusing arrow function syntax

5. You want to build a dApp interface that shows a user's token balance and lets them send tokens. Which approach best improves usability?

hard

A. Display raw blockchain data and require manual transaction input

B. Create a clear UI showing balance and simple send button with feedback

C. Only provide a command-line interface for advanced users

D. Hide all blockchain info and send tokens automatically without user input

Solution

1. Step 1: Identify usability goals for dApp UI

   Users need clear info and easy controls to interact confidently with tokens.

2. Step 2: Evaluate options for user friendliness

   Create a clear UI showing balance and simple send button with feedback offers clear balance display, simple send button, and feedback, improving usability.

3. Final Answer:

   Create a clear UI showing balance and simple send button with feedback -> Option B

4. Quick Check:

   Clear UI + simple controls = better usability [OK]

Hint: Clear info and simple buttons improve dApp usability [OK]

Common Mistakes:

• Forcing users to handle raw blockchain data
• Using only command-line interfaces
• Hiding important info or controls