Blockchain Smart Contracts and dApps Questions and Answers

Question 1

A development team is building a decentralized application (dApp) and needs to choose a JavaScript library to facilitate interaction with the Ethereum blockchain.
They prioritize a smaller library size for faster loading times, a more modern API design using Promises and async/await, and strong TypeScript support.
Which library would be the most suitable choice?

Accepted Answer

Ethers.js

Answer

Web3.js

Answer

Truffle.js

Answer

Ganache.js

Question 2

A smart contract requires real-world data, such as the current price of a commodity, to execute its logic. Blockchains cannot natively access off-chain information. What is the standard solution for securely feeding external data into a smart contract?

Accepted Answer

A decentralized oracle network.

Answer

A centralized API call from within the smart contract.

Answer

A hardcoded data feed updated by the contract owner.

Answer

An inter-blockchain communication protocol.

Question 3

A developer deploys a smart contract but soon discovers a critical bug. Due to the immutability of the blockchain, the contract code cannot be changed. Which design pattern allows developers to update contract logic while preserving the contract's address and state?

Accepted Answer

The Proxy Pattern

Answer

The Singleton Pattern

Answer

The Factory Pattern

Answer

The Observer Pattern

Question 4

Which of the following best describes the core function of a Decentralized Autonomous Organization (DAO)?

Accepted Answer

An organization governed by rules encoded as smart contracts on a blockchain.

Answer

A legal framework for registering blockchain-based companies.

Answer

A marketing collective for promoting dApps and crypto projects.

Answer

A centralized company that uses cryptocurrency for payroll.

Question 5

A DeFi protocol's smart contract has a function that (1) checks a user's balance, (2) sends them their requested funds, and then (3) updates their balance. An attacker exploits this by creating a malicious contract that, upon receiving funds, immediately calls the withdrawal function again before the original call can update the balance. This vulnerability is known as a:

Accepted Answer

Reentrancy Attack

Answer

Integer Overflow Attack

Answer

Timestamp Dependence Attack

Answer

Denial of Service Attack

Question 6

In the context of Ethereum, what is the primary purpose of 'gas'?

Accepted Answer

To act as a unit of measurement for the computational work required to execute transactions and smart contracts.

Answer

To measure the physical energy consumption of the network.

Answer

A token used for voting in network governance proposals.

Answer

A protocol for compressing transaction data to save block space.