A Course Workspace That Never Touches Your Disk

The lesson workspace on this site loads starter code from the database into three editable panels, runs it in a sandboxed iframe, and never writes anything to localStorage or cookies. Refresh the page and you are back to the starter snippet.

That is a deliberate constraint, not an oversight: it keeps the exercise stateless, keeps the codebase simple, and avoids raising expectations that work will be saved without an account system attached to it.

How the sandbox works

A hidden <iframe sandbox> receives a freshly assembled HTML document — the HTML panel content, a <style> block from the CSS panel, and a <script> block from the JS panel — every time the Run button is pressed.