All runtime differences are quite neglectable if you use typescript, at least in my experience. You never accidentally use unassigned variables in typescript. A

All runtime differences are quite neglectable if you use typescript, at least in my experience. You never accidentally use unassigned variables in typescript. Also, `{ x: undefined }` and `{}` are distinguishable. Undefined plays well together with optional fields in typescript, null does not and requries normalization! `undefined` in a JSON array is a problem though.