Read .2bit files in node or webpack


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420May 25, 2021Jul 24, 2018Minified + gzip package size for @gmod/twobit in KB



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Read .2bit sequence files using pure JavaScript, works in node or in the browser.


$ npm install --save @gmod/twobit


const { TwoBitFile } = require('@gmod/twobit')
const t = new TwoBitFile({
  path: require.resolve('./data/foo.2bit'),

// get the first 10 bases of a sequence from the file.
// coordinates are UCSC standard 0-based half-open
const chr1Region = await t.getSequence('chr1', 0, 10)
// chr1Region is now a string of bases, 'ACTG...'

// get a whole sequence from the file
const chr1Bases = await t.getSequence('chr1')

// get object with all seq lengths as { seqName => length, ... }
const allSequenceSizes = await t.getSequenceSizes()

// get the size of a single sequence
const chr1Size = await t.getSequenceSize('chr1')

// get an array of all sequence names in the file
const seqNames = await t.getSequenceNames()



Table of Contents


  • args object
    • args.filehandle Filehandle? node fs.promises-like filehandle for the .2bit file. Only needs to support filehandle.read(buffer, offset, length, position)
    • args.path string? filesystem path for the .2bit file to open
    • args.seqChunkSize


Returns Promise for object with the file's header information, like { magic: 0x1a412743, version: 0, sequenceCount: 42, reserved: 0 }


Returns Promise for object with the file's index of offsets, like { seqName: fileOffset, ...}


Returns Promise for an array of string sequence names that are found in the file


Returns Promise for an object listing the lengths of all sequences like {seqName: length, ...}


  • seqName string name of the sequence

Returns Promise for the sequence's length, or undefined if it is not in the file


  • seqName string name of the sequence you want
  • regionStart number? optional 0-based half-open start of the sequence region to fetch. (optional, default 0)
  • regionEnd number? optional 0-based half-open end of the sequence region to fetch. defaults to end of the sequence

Returns Promise for a string of sequence bases

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.


MIT © Robert Buels

If you find any bugs or have a feature request, please open an issue on github!

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