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

Question

RepoPilot · Accepted Answer

The `prettyBytes` function formats byte counts into human-readable strings through a multi-step process [index.js:L124-L179]:

**1. Input Validation & Options Setup**
The function first validates that the input is a finite number or bigint [index.js:L125-L127]. It then merges user options with defaults, setting `bits`, `binary`, `space`, and `nonBreakingSpace` [index.js:L129-L134].

**2. Unit Selection**
Based on the options, the function selects the appropriate unit array [index.js:L136-L139]:
- `BYTE_UNITS` (default): 'B', 'kB', 'MB', 'GB', etc. [index.js:L1-L9]
- `BIBYTE_UNITS`: 'B', 'KiB', 'MiB', 'GiB', etc. for binary format [index.js:L11-L19]
- `BIT_UNITS`: 'b', 'kbit', 'Mbit', 'Gbit', etc. for bits [index.js:L21-L29]
- `BIBIT_UNITS`: 'b', 'kibit', 'Mibit', 'Gibit', etc. for binary bits [index.js:L31-L39]

**3. Sign Handling**
For negative numbers, it extracts the sign prefix and converts to positive for processing [index.js:L147-L150]. It also handles the signed zero case specially [index.js:L141-L145].

**4. Exponent Calculation**
For numbers ≥ 1, it calculates the appropriate exponent (which unit to use) using either base-1024 (binary) or base-1000 (SI prefix) [index.js:L158].

**5. Formatting & Localization**
The number is scaled by dividing by 1000^exponent (or 1024^exponent for binary) [index.js:L159]. If no locale is specified, precision is adjusted to maintain significant digits [index.js:L161-L163]. The number is then formatted as a locale string if a locale is provided [index.js:L165].

**6. Assembly & Padding**
Finally, it combines the prefix, formatted number, separator (space or non-breaking space), and unit into the result [index.js:L166-L167]. If `fixedWidth` is specified, padding is applied for alignment [index.js:L169].

**Example**: `prettyBytes(1337)` yields `'1.34 kB'` because 1337 ÷ 1000 ≈ 1.34, formatted with the 'kB' unit.

FOLLOW_UPS:
- What options does prettyBytes support?
- How does the binary option differ from default behavior?
- How does locale formatting work in prettyBytes?