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TypeScript ships with 15+ utility types that let you derive new types from existing ones. Here's the full toolkit with the production patterns you'll actually reach for.

Build Node.js's EventEmitter from scratch in 100 lines. Learn why listener removal requires saved references, how once() wraps callbacks, and what that MaxListenersExceededWarning actually means.

Two mid-to-senior linked list problems that test data structure design: deep-copying a list with random pointers (O(1) space trick), and implementing LRU Cache in O(1).

Sliding window maximum is the classic follow-up to every sliding window problem. Learn the monotone deque pattern in JavaScript with LeetCode 239, 1438, and 1696.

Stop writing the same function for every type or reaching for `any`. TypeScript generics let you write it once — with full type inference, constraints, and zero casting.

LC 297 is a Hard but the insight is simple: null markers make any traversal unambiguous. Learn preorder DFS and BFS serialization, plus the BST shortcut for LC 449.

Stop casting with `as` and `!`. Discriminated unions give TypeScript enough information to narrow types automatically — making impossible states unrepresentable and exhaustiveness checking free.

Caddy gives you automatic HTTPS and a 4-line config. Nginx gives you raw throughput and a 25-year ecosystem. Here's when each one is the right call.

Jump Game, Gas Station, and Partition Labels — three greedy DSA patterns that feel like guesswork until you see the invariant that makes each one provably correct.