@gmod/tabix

Read Tabix-indexed files using either .tbi or .csi indexes.

Install

npm install @gmod/tabix

Usage

import { TabixIndexedFile } from '@gmod/tabix'

// Local file — TBI index assumed at path + '.tbi'
const file = new TabixIndexedFile({ path: 'file.vcf.gz' })

// CSI index
const file = new TabixIndexedFile({
  path: 'file.vcf.gz',
  csiPath: 'file.vcf.gz.csi',
})

// Remote files
const file = new TabixIndexedFile({
  url: 'https://example.com/file.vcf.gz',
  tbiUrl: 'https://example.com/file.vcf.gz.tbi',
})

// Or with a filehandle from generic-filehandle2
import { RemoteFile } from 'generic-filehandle2'

const file = new TabixIndexedFile({
  filehandle: new RemoteFile('https://example.com/file.vcf.gz'),
  tbiFilehandle: new RemoteFile('https://example.com/file.vcf.gz.tbi'),
})

getLines

Fetches lines overlapping a region. start/end are 0-based half-open coordinates (unlike the tabix CLI which uses 1-based closed).

const lines: string[] = []
await file.getLines('chr1', 200, 300, line => lines.push(line))

The callback also receives the virtual file offset and parsed coordinates for the line:

await file.getLines('chr1', 200, 300, (line, fileOffset, start, end) => {
  lines.push(line)
})

Pass an options object to use an AbortSignal:

const aborter = new AbortController()
await file.getLines('chr1', 200, 300, {
  lineCallback: (line, fileOffset, start, end) => lines.push(line),
  signal: aborter.signal,
})

Notes:

• Meta/comment lines are skipped
• Line strings have no trailing whitespace
• Pass undefined for end to read to the end of the contig

Without NPM (CDN)

<script src="https://unpkg.com/@gmod/tabix/dist/tabix-bundle.js"></script>

See example/index.html for a working demo.

API

new TabixIndexedFile(args)

getLines(refName, start, end, opts)

Calls opts (or opts.lineCallback) for each line overlapping [start, end).

Callback signature: (line: string, fileOffset: number, start: number, end: number) => void

getHeader(opts?): Promise<string>

Returns all comment/meta lines before the first data line as a string.

getHeaderBuffer(opts?): Promise<Uint8Array>

Returns the header as raw bytes.

getReferenceSequenceNames(opts?): Promise<string[]>

Returns reference sequence names in index order. renameRefSeqs is not applied to these names.

lineCount(refName, opts?): Promise<number>

Returns the number of data lines on the given reference, or -1 if the reference is not in the index.

bytesForRegions(regions, opts?): Promise<number>

Estimates the compressed byte size of index chunks covering the given regions. Useful for deciding whether a request is too large before calling getLines.

Publishing

Trusted publishing via GitHub Actions.

pnpm version patch  # or minor/major

Academic Use

This package was written with funding from the NHGRI as part of the JBrowse project. If you use it in an academic project that you publish, please cite the most recent JBrowse paper, which will be linked from jbrowse.org.

License

MIT © Robert Buels