@votingworks/ballot-encoder

Ballot Encoder

Provides encoding and decoding services for completed ballots.

Dev Install

To use within VS Code:

yarn install
yarn pnpify --sdk

Developing Alongside another Project

In dev ballot-encoder dir, run yarn tsc to generate JavaScript files.

In the PROJECT you wish to use this dev version of ballot-encoder:

1. cd path/to/PROJECT/node_modules/@votingworks
2. rm -rf ballot-encoder
3. ln -s path/to/ballot-encoder ballot-encoder
4. restart project server if applicable

Example

import {
  decodeBallot,
  electionSample as election,
  encodeBallot,
  getContests,
  vote,
} from '@votingworks/ballot-encoder'

const ballotStyle = election.ballotStyles[0]
const precinct = election.precincts[0]
const ballotId = 'abcde'
const contests = getContests({ ballotStyle, election })
const votes = vote(contests, {
  'judicial-robert-demergue': 'yes',
  'judicial-elmer-hull': 'yes',
  'question-a': 'yes',
  'question-b': 'no',
  'question-c': 'yes',
  'proposition-1': 'yes',
  'measure-101': 'no',
  '102': 'yes',
})
const ballot = {
  election,
  ballotId,
  ballotStyle,
  precinct,
  votes,
}

console.log(encodeBallot(ballot))
/*
Uint8Array [
  86, 88,  1,  2,  49,  50,  2,
  50, 51,  0, 15, 254, 208, 86,
  22, 38, 54, 70,  80
]
*/

console.log(decodeBallot(election, encodeBallot(ballot)).ballot.votes)
/*
{
  '102': 'yes',
  'judicial-robert-demergue': 'yes',
  'judicial-elmer-hull': 'yes',
  'question-a': 'yes',
  'question-b': 'no',
  'question-c': 'yes',
  'proposition-1': 'yes',
  'measure-101': 'no'
}
*/

Usage

To encode a ballot, simply pass a completed ballot object to encodeBallot. You'll get back a buffer that may be stored or transmitted and later passed to decodeBallot with the same election data that was part of the completed ballot object.

There are multiple encoder versions and by default the latest will be used when encoding. To specify the version, pass the EncoderVersion as the second parameter to encodeBallot:

import { encodeBallot, EncoderVersion } from '@votingworks/ballot-encoder'

const encodedBallot = encodeBallot(ballot, EncoderVersion.v1)

When decoding, you may pass an EncoderVersion or you may allow decodeBallot to detect the encoder version:

import { decodeBallot, EncoderVersion } from '@votingworks/ballot-encoder'

// automatically detect version
const result = decodeBallot(election, encodedBallot)
console.log('Ballot version:', result.version)
console.log('Ballot:', result.ballot)

// specify version
const result = decodeBallot(election, encodedBallot, EncoderVersion.v0)
console.log('Ballot version:', result.version)
console.log('Ballot:', result.ballot)

If you only want to detect the version, you can simply use detect:

import { detect } from '@votingworks/ballot-encoder'

const version = detect(encodedBallot)
console.log('Ballot version:', version)