JSON tree rendering (recurse on values), file explorer (recurse on children), nested comments (recurse on replies), deep clone (recurse on object properties), and DOM traversal (recurse on childNodes). Any nested or self-similar structure.

function deepClone(obj) { if (obj === null || typeof obj !== 'object') return obj; const clone = Array.isArray(obj) ? [] : {}; Object.keys(obj).forEach(key => clone[key] = deepClone(obj[key])); return clone; }

function renderComment(comment, depth) { /* render comment */ comment.replies.forEach(reply => renderComment(reply, depth + 1)); }. Each comment recurses into its replies, indenting by depth.