Short answer: type the number, pick the base it is written in, and see it in binary, octal, decimal, hex and base36. Bit grouping and byte length are included because that is what you actually check against a register, a flag or a binary protocol.
Where each base shows up
- Binary — permission bits, flags, protocol headers.
- Octal — legacy file modes and some Unix dumps.
- Decimal — ids, counters, anything a database stores.
- Hex — colours, hashes, memory addresses, byte literals.
- Base36 — short public identifiers from a numeric key.
Why precision is the interesting part
A 64-bit id is larger than JavaScript's safe integer range. A converter that parses toNumber and prints back loses the last digits and gives you a plausible wrong answer — the kind of bug that shows up as "user not found" in production. BigInt keeps every digit, and the byte count tells you whether the value fits in 4 bytes, 8 bytes or neither.