Chord JS

Chord JS is a music theory package that identifies notes, chords, and key signatures on an 88-key piano.

To install run

npm install @patrady/chord-js

or if you're using yarn

yarn add @patrady/chord-js

Chords

To translate a series of notes into a chord, use

import { Chord } from '@patrady/chord-js';

const chord = new Chord.for('C E G');

chord?.getName(); // C

This table shows the type of supported chords with examples

| Chord | Example | | -------------------------------------------------------------------------------------- | ---------------------------------- | | Major | Chord.for("C E G"); // C | | Minor | Chord.for("C Eb G"); // Cm | | Suspended | Chord.for("C F G"); // Csus | | Suspended Second | Chord.for("C D G"); // Csus2 | | Augmented | Chord.for("C E G#"); // Caug | | Diminished | Chord.for("C Eb Gb"); // Cdim | | Inverted | Chord.for("E G C"); // C/E | | Sixth | Chord.for("C E G A"); // C6 | | Minor Sixth | Chord.for('C Eb G A'); // Cm6 | | Dominant Seventh | Chord.for("C E G Bb"); // C7 | | Diminished Seventh | Chord.for("C Eb Gb A"); // Cdim7 | | Augmented Seventh | Chord.for("C E G# Bb"); // C+7 | | Major Seventh | Chord.for("C E G B"); // Cmaj7 | | Augmented Major Seventh | Chord.for("C E G# B"); // Cmaj+7 | | Minor Seventh | Chord.for("C Eb G Bb"); // Cm7 | | Minor Major Seventh | Chord.for("C Eb G B"); // Cm7+ | | Half-Diminished Seventh | Chord.for("C Eb Gb Bb"); // Cø7 |

Key Signatures

A Key Signature is a combination of sharps and flats at the beginning of each stave.

import { Note, KeySignatureOfD } from '@patrady/chord-js';

new KeySignatureOfD().getNotes(); // D, E, F#, G, A, B, C#, D

new KeySignatureOfD().normalize(new Note('Gb')); // F#

new KeySignatureOfD().isInKey(new Note('Gb')); // false
new KeySignatureOfD().isInKey(new Note('F#')); // true

| Attribute | Description | Example | | ----------------- | ---------------------------------------------------------------------- | --------------------------------------------------------------- | | getNotes() | Returns an array of eight notes from the base to the octave. | new KeySignatureOfD().getNotes(); // D, E, F#, G, A, B, C#, D | | normalize(note) | Normalizes a note from one key signature to the current key signature. | new KeySignatureOfD().normalize(new Note("Gb")); // F# | | isInKey(note) | Returns whether a note is in the key signature | new KeySignatureOfD().isInKey(new Note("Gb")); // false |

Supported Key Signatures

The major key signatures are supported but less popular ones are not. Check this table to see if the one you need is supported:

| Key Signature | Supported | Name | | ------------- | --------- | ---------------------- | | C | ✅ | KeySignatureOfC | | Cb | ❌ | | | C# | ❌ | | | D | ✅ | KeySignatureOfD | | Db | ✅ | KeySignatureOfDb | | D# | ❌ | | | E | ✅ | KeySignatureOfE | | Eb | ✅ | KeySignatureOfEb | | E# | ❌ | | | F | ✅ | KeySignatureOfF | | Fb | ❌ | | | F# | ✅ | KeySignatureOfFsharp | | G | ✅ | KeySignatureOfG | | Gb | ✅ | KeySignatureOfGb | | G# | ❌ | | | A | ✅ | KeySignatureOfA | | Ab | ✅ | KeySignatureOfAb | | A# | ❌ | | | B | ✅ | KeySignatureOfB | | Bb | ✅ | KeySignatureOfBb | | B# | ❌ | |

Notes

A Note is the fundamental element of music. Notes are simply frequencies and are used to create chords and key signatures.

import { Note } from '@patrady/chord-js';

const note = new Note('Eb4');

| Attribute | Description | Example | | --------------------- | -------------------------------------------------------------------------------------------------- | ----------------------------------- | | getName() | The name of the note and accidental | note.getName(); // Eb | | getScientificName() | The name of the note, accidental, and octave | note.getScientificName(); // Eb4 | | getOctave() | The octave between 0 and 8 | note.getOctave(); // 4 | | getFrequency() | The frequency in Hz, up to 5 decimal places | note.getFrequency(); // 311.12698 | | getKeyNumber() | The number of the key on an 88-key piano | note.getKeyNumber(); // 43 | | getMidiValue() | The MIDI note of the key on an 88-key piano | note.getMidiValue(); // 63 |

MIDI Keyboard

When interacting with a MIDI keyboard and you want to convert a MIDI value to a note, use

import { Note } from '@patrady/chord-js';

const note = Note.fromMidi(24);

note.getScientificName(); // C1

For enharmonic notes, the MIDI value will be the same. For example, C# and Db in the 1st octave will have the same MIDI value of 25. To choose a specific enharmonic, normalize the note to a key signature:

import { Note, KeySignatureOfD, KeySignatureOfDb } from '@patrady/chord-js';

const note = Note.fromMidi(25);

new KeySignatureOfD().normalize(note); // C#
new KeySignatureOfDb().normalize(note); // Db

A chord can also be determined from the MIDI notes like so

import { Note } from '@patrady/chord-js';

const C = Note.fromMidi(60);
const E = Note.fromMidi(64);
const G = Note.fromMidi(67);

Chord.for([C, E, G])?.getName(); // C