Immutability

Deep Clone with structuredClone

Deep cloning is no longer a `JSON.parse(JSON.stringify(x))` hack. Modern runtimes ship `structuredClone`, which handles cycles, Maps, Sets, typed arrays, and Date out of the box. This snippet shows the canonical built-in usage, the JSON fallback for legacy code paths and its real limits, and a hand-rolled recursive clone for when you need to skip specific keys or types. Pick the right tool and stop carrying lodash for one helper.

Freeze, Seal, and preventExtensions on Objects

JavaScript ships three integrity levels for objects (`Object.preventExtensions`, `Object.seal`, and `Object.freeze`) and they are easy to confuse because each silently relaxes one rule from the next. This snippet builds them up from least to most restrictive, shows the strict-mode behavior that turns silent failures into errors, and finishes with a recursive `deepFreeze` for nested config. Reach for these when you want a runtime guarantee that downstream code cannot mutate a shared object.

JavaScript Object Reference and Key Coercion Traces

Six traces covering object-key stringification, reference vs literal equality, `Object.create` prototype chains, and shallow-copy aliasing with arrays.

JavaScript Immutability and References Quiz

Lock down objects with `Object.freeze`, build read-only properties with `Object.defineProperty`, and reason about why React leans on immutable updates.

JavaScript Immutable Object Key Removal: Two Approaches Quiz

Two seeded approaches to remove an object key without mutation (spread + delete, reduce + filter), plus two companions on destructure-and-drop and a deep-clone caveat.