Object.keys(obj).length === 0 is the safest plain-object emptiness check in modern JavaScript: it inspects only own enumerable string keys, which matches what JSON serialisation cares about. The obj != null && typeof obj === 'object' guard rejects null, undefined, primitives, and arrays-or-string thrown at it by accident. The cost is one transient array allocation; for steady-state hot paths see the next accordion. This is the version to default to in app code.

When the check fires inside a hot render loop, Object.keys allocates an array just to read its length, which is wasteful. The for..in loop with Object.hasOwn short-circuits on the very first own key, so emptiness checks become O(1) on the common non-empty path. The Object.hasOwn filter also correctly ignores inherited properties from the prototype chain, which is what almost everyone means by "empty". Reach for this version in performance-sensitive code; the simpler Object.keys form is fine elsewhere.

Form validation, default-value resolution, and feature-flag rollouts almost always need a single isEmpty that handles every container type. The branch order matters: null/undefined first (so later checks can assume non-nullish), then length-bearing types, then Map/Set whose count lives on size, then plain objects. Numbers and booleans return false deliberately because 0 and false are values, not empty containers. This is the helper that replaces a half-dozen if chains across a codebase.