NextCode is the interactive coding engine inside NextDeveloper. It includes a full code editor that looks and behaves like the tools professional developers use every day.
Editor features
- Monaco editor: syntax highlighting, line numbers, auto-indent, and familiar keyboard shortcuts.
- File tabs: some lessons include multiple files; switch between them with tabs.
- Run button: executes your code and shows the output in the console panel.
- Tests panel: automated tests tell you whether your solution passes.
- Preview panel: for HTML/CSS/JS lessons, see the rendered output live.
- Hint panel: targeted hints and, when available, solution hints that can insert code for you.
How code runs
Code runs in one of two ways, depending on the lesson:
- In-browser sandbox: JavaScript, TypeScript, and HTML lessons execute in a sandboxed iframe in your browser for fast feedback. JSX and TypeScript are compiled with Babel before running.
- WebContainer: for Node.js and backend lessons, code runs in a browser-based Node.js environment. This requires cross-origin isolation (COOP/COEP), which the app adds automatically for lesson pages.
SQL lessons run an in-memory SQL executor directly in the browser.
Tips for a smooth experience
- Save your work by pressing Run. Progress is recorded when tests pass.
- Read the error message carefully. It usually points to the exact line.
- Use the Hint button if you are stuck. Solution hints will insert code when you choose to reveal them.
- If the editor says “Babel/React is still loading,” wait a moment and click Run again.
- If the editor feels slow, try closing other browser tabs or disabling heavy browser extensions.
Common next steps
- Learn how feedback works in Practice Problems.
- Fix running issues in Troubleshooting.