JavaScript API Reference

Initialization

init(options?)

Loads and initializes the WASM module. Must be called before creating any BachGenerator instances.

import { init } from '@libraz/midi-sketch-bach'

// Node.js (WASM path resolved automatically)
await init()

// Browser (specify WASM path)
await init({ wasmPath: '/wasm/midisketch.wasm' })

Parameters:

Parameter	Type	Description
options.wasmPath	string	Path to the .wasm file. Required in browser environments.

Returns: Promise<void>

---

BachGenerator

The main class for generating Bach-style compositions.

Constructor

const generator = new BachGenerator()

Creates a new generator instance. Call init() before creating any instances.

generate(config?)

Generates a composition based on the provided configuration.

generator.generate({
  form: 'fugue',
  key: 2,
  isMinor: true,
  numVoices: 4,
  bpm: 80,
  seed: 42
})

Parameters: See BachConfig below.

Returns: void

getMidi()

Returns the generated composition as Standard MIDI File data.

const midi = generator.getMidi()
// midi is a Uint8Array containing a valid .mid file

Returns: Uint8Array

getEvents()

Returns structured event data with metadata and individual note events.

const events = generator.getEvents()
console.log(events.form)        // "Fugue"
console.log(events.key)         // "D minor"
console.log(events.bpm)         // 80
console.log(events.total_bars)  // 32
console.log(events.tracks)      // Array of TrackData

Returns: EventData

getInfo()

Returns information about the generator and its current state.

const info = generator.getInfo()

Returns: BachInfo

destroy()

Frees WASM memory allocated by this generator. Always call this when done.

generator.destroy()

WARNING

After calling destroy(), the generator instance must not be used again. Create a new BachGenerator if you need to generate another piece.

---

BachConfig

Configuration object passed to generate(). All fields are optional.

Field	Type	Default	Description
form	number | string	0	Musical form (0--8 or name). See Forms and Presets Reference.
key	number	0	Key (0--11 pitch class: 0=C, 1=C#, 2=D, ... 11=B)
isMinor	boolean	false	Minor key when true, major when false
numVoices	number	Form default	Number of voices (2--5)
bpm	number	100	Tempo in BPM (40--200, 0 uses default of 100)
seed	number	0	Random seed (0 = random)
character	number | string	0	Subject character type (0--3)
instrument	number | string	Form default	Instrument preset (0--5)
scale	number | string	1	Duration scale (0=short, 1=medium, 2=long, 3=full)
targetBars	number	--	Target bar count (overrides scale)

Form Values

Forms can be specified by number or name string:

Number	String
0	"fugue"
1	"prelude-and-fugue"
2	"trio-sonata"
3	"chorale-prelude"
4	"toccata-and-fugue"
5	"passacaglia"
6	"fantasia-and-fugue"
7	"cello-prelude"
8	"chaconne"

Instrument Values

Number	String
0	"organ"
1	"harpsichord"
2	"piano"
3	"violin"
4	"cello"
5	"guitar"

Character Values

Number	Description
0	Default balanced
1	Lyrical, stepwise
2	Energetic, wider intervals
3	Dramatic, rhythmically varied

Scale Values

Number	String	Description
0	"short"	Compact
1	"medium"	Standard (default)
2	"long"	Extended
3	"full"	Maximum length

---

Response Types

EventData

interface EventData {
  form: string          // Form name (e.g., "Fugue")
  key: string           // Key description (e.g., "D minor")
  bpm: number           // Tempo
  seed: number          // Seed used for generation
  total_ticks: number   // Total duration in MIDI ticks
  total_bars: number    // Total bar count
  description: string   // Human-readable description
  tracks: TrackData[]   // Array of track data
}

TrackData

interface TrackData {
  name: string          // Track name (e.g., "Soprano", "Bass")
  channel: number       // MIDI channel (0-15)
  program: number       // General MIDI program number
  note_count: number    // Number of notes in this track
  notes: NoteEvent[]    // Array of note events
}

NoteEvent

interface NoteEvent {
  pitch: number         // MIDI note number (0-127)
  velocity: number      // Note velocity (0-127)
  start_tick: number    // Start time in MIDI ticks
  duration: number      // Duration in MIDI ticks
  voice: number         // Voice index
}

---

Preset Enumeration Functions

These functions return arrays of PresetInfo objects describing available options.

getForms()

import { getForms } from '@libraz/midi-sketch-bach'

const forms = getForms()
// [{ index: 0, name: "Fugue", ... }, ...]

getInstruments()

import { getInstruments } from '@libraz/midi-sketch-bach'

const instruments = getInstruments()
// [{ index: 0, name: "Organ", ... }, ...]

getCharacters()

import { getCharacters } from '@libraz/midi-sketch-bach'

const characters = getCharacters()

getKeys()

import { getKeys } from '@libraz/midi-sketch-bach'

const keys = getKeys()
// [{ index: 0, name: "C", ... }, { index: 1, name: "C#", ... }, ...]

getScales()

import { getScales } from '@libraz/midi-sketch-bach'

const scales = getScales()
// [{ index: 0, name: "Short", ... }, ...]

getVersion()

import { getVersion } from '@libraz/midi-sketch-bach'

const version = getVersion()
// "1.0.0"

---

Complete Examples

Generate and Save a Fugue

import { init, BachGenerator } from '@libraz/midi-sketch-bach'
import { writeFileSync } from 'fs'

await init()

const generator = new BachGenerator()
generator.generate({
  form: 'fugue',
  key: 2,
  isMinor: true,
  numVoices: 4,
  bpm: 76,
  seed: 12345
})

writeFileSync('fugue-d-minor.mid', generator.getMidi())

const events = generator.getEvents()
console.log(`Generated: ${events.description}`)
console.log(`Bars: ${events.total_bars}, Tracks: ${events.tracks.length}`)

for (const track of events.tracks) {
  console.log(`  ${track.name}: ${track.note_count} notes`)
}

generator.destroy()

Generate All Forms

import { init, BachGenerator, getForms } from '@libraz/midi-sketch-bach'
import { writeFileSync } from 'fs'

await init()

const forms = getForms()
const generator = new BachGenerator()

for (const form of forms) {
  generator.generate({
    form: form.index,
    key: 2,
    isMinor: true,
    seed: 42
  })

  const filename = `bach-${form.name.toLowerCase().replace(/\s+/g, '-')}.mid`
  writeFileSync(filename, generator.getMidi())
  console.log(`Saved: ${filename}`)
}

generator.destroy()

Browser: Generate and Download

import { init, BachGenerator } from '@libraz/midi-sketch-bach'

await init({ wasmPath: '/wasm/midisketch.wasm' })

const generator = new BachGenerator()
generator.generate({
  form: 'fugue',
  key: 0,
  isMinor: false
})

const midi = generator.getMidi()
const blob = new Blob([midi], { type: 'audio/midi' })
const url = URL.createObjectURL(blob)

const a = document.createElement('a')
a.href = url
a.download = 'bach-fugue.mid'
a.click()

URL.revokeObjectURL(url)
generator.destroy()