Data Types

Int, float, decimal — and why 0.1 + 0.2 isn't 0.3.

Array, list, map, set, tuple — when to reach for each.

Aliasing, shallow copy, mutation through a handle.

null, undefined, NaN — three ways to say 'no value'.

UTF-8, UTF-16, surrogates, graphemes — why string length is a trick question.

Wall-clock vs monotonic, UTC always, ISO-8601, and the rules that save you from DST.

Bytes, buffers, byte order — and the line between text and bytes.

Persistent collections, structural sharing, referential equality — the win and the cost.

JSON, Protobuf, MessagePack, CBOR, Avro — wire size vs CPU vs schema evolution.