Spectra

Spectra is the iterable collection of Spectrum instances exposed by every file:

f.spectra;                  // Spectra
f.spectra[0];               // first Spectrum
f.spectra[42];              // 43rd Spectrum
f.spectra.length;           // number
for (const s of f.spectra) { /* in scan order */ }

Spectrum properties

Property	Type	Notes
index	number	Position in the file
scan	number	Original scan number
msLevel	number	1, 2, ...
retentionTime	number	seconds
size	number	Peak count
mz	Float32Array \| Float64Array	Lazy — read triggers one block decompress
intensity	Float32Array \| Float64Array	Lazy
xml	string	Spectrum XML element

mz and intensity are computed lazily on first access. Iterating f.spectra without touching either is cheap; touching s.mz is a single block decompression.

Iteration patterns

// MS2 spectra
const ms2 = [...f.spectra].filter(s => s.msLevel === 2);

// A scan range
for (let i = 1000; i < 2000; i++) {
  const s = f.spectra[i];
  ...
}

For complex selections, prefer the extraction guide — it pushes the filter into the C core.