Full-Stack Blockchain Assessment

This is a project for blockchain developers. Candidates fix bugs and add missing code across smart contract simulation, backend APIs, and frontend.

Assessment Details

• Duration: 12 hours from the time you receive invitation from GitHub.

• Format: Take-home project

• Submission: Upon completion, make a public repository, submit your deliverables with your name on GitHub and contact gauge@crewspacex.com

Stack

• Frontend: TypeScript, Vite, React
• Backend: Node.js, CommonJS, Express
• Contracts: In-memory JS simulation (TokenVault-style contract)

Run the project

From the repo root:

npm install
npm run dev

A single npm run dev starts both the backend and the frontend. Backend runs at http://localhost:3001, frontend at http://localhost:5173 with API proxy to the backend.

Assessment tasks (for candidates)

The assessment includes: the wallet API returns a non-JSON-serializable balance so the Wallet section fails at runtime when fetching balance; the contract balance endpoint returns a non-JSON-serializable value so the Contract section fails at runtime when fetching balance; the chain blocks endpoint returns the first N blocks instead of the latest N, so the Chain section shows the wrong blocks until the route is fixed and the frontend passes the limit.

1. Backend - Wallet API
   Fix the response so the frontend can display the wallet balance.

2. Backend - Contract balance
   The TokenVault balanceOf result includes a non-JSON-serializable value. Return the contract balance in a JSON-safe format.

3. Backend - Withdraw access control
   In TokenVault.withdraw, ensure only the contract owner can call withdraw. Return a clear error for unauthorized callers.

4. Backend - Chain blocks
   GET /api/chain/blocks?limit=N should return the latest N blocks (e.g. last 5), not the first N. Fix the route logic.

5. Backend - Error handling
   Add a global Express error handler that responds with { error: message } and status 500 for unhandled errors.

6. Frontend - Wallet display
   The wallet balance from the API may be a string or number. Ensure the Wallet section always displays the balance correctly (no [object Object] or serialization issues).

7. Frontend - Chain section
   When fetching “latest blocks”, pass the limit (e.g. 5) to the API so the backend returns the correct slice. Use the existing limit variable in the component.

Candidates should fix the above so that:

• Backend stays running and all listed endpoints behave correctly.
• Frontend can check health, view wallet balance, view/use contract deposit/withdraw, and list latest blocks without errors.