How does pretty-bytes format byte counts into a human-readable string?

The pretty-bytes library converts byte counts to human-readable strings by determining the appropriate unit (B, kB, MB, GB, etc.) and then scaling the number accordingly.

Core Formatting Process

The main function [index.js:L124-L179] implements the following logic:

1. Input Validation: It first checks that the input is a valid finite number or bigint.

2. Unit Selection: Based on the options provided (bits, binary), it selects from one of four unit arrays [index.js:L1-L42]:

   • BYTE_UNITS: Standard byte units (B, kB, MB, GB, TB, PB, EB, ZB, YB)
   • BIBYTE_UNITS: Binary byte units (B, KiB, MiB, GiB, TiB, PiB, EiB, ZiB, YiB)
   • BIT_UNITS: Standard bit units (b, kbit, Mbit, Gbit, etc.)
   • BIBIT_UNITS: Binary bit units (b, kibit, Mibit, Gibit, etc.)

3. Exponent Calculation: For numbers ≥ 1, it calculates which unit level to use via the exponent, using either base-10 (1000) or base-2 (1024) depending on the binary option [index.js:L160].

4. Number Scaling: The original number is divided by the appropriate power (1000^exponent or 1024^exponent) to get a manageable decimal value.

5. Localization: The scaled number is formatted using toLocaleString() if a locale option is specified, otherwise precision is adjusted to show meaningful digits.

6. Assembly: The result combines the prefix (sign), formatted number, optional separator (space or non-breaking space), and unit string.

For example, 1337 bytes becomes 1.34 kB because 1337 ÷ 1000¹ = 1.337, which is formatted as 1.34 with the kB unit.

FOLLOW_UPS:

• What options can customize the formatting behavior?
• How does the binary option differ from standard formatting?
• What happens with numbers smaller than 1?