Get music key (scale) from notes used in it

README.md

Usage

1. Install Deno
2. Run

deno run https://gist.githubusercontent.com/5t111111/698c87f8ee518f4db737bd00502695f1/raw/get-music-key-from-notes.ts C E F

The above will output:

{ candidates: [ "C", "F", "Dm", "Am" ] }

get-music-key-from-notes.ts

/*
 * Get music key (scale) from notes used
 *
 * Usage:
 *
 * deno run https://gist.githubusercontent.com/5t111111/698c87f8ee518f4db737bd00502695f1/raw/get-music-key-from-notes.ts C E F
 *
 * The above example shows you `{ candidates: [ "C", "F", "Dm", "Am" ] }`
 */

const notes = ["C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B"];

const majorIntervals = [0, 2, 2, 1, 2, 2, 2];
const majorIntervalsFromRoot = majorIntervals.map((interval, idx) =>
  majorIntervals.slice(0, idx + 1).reduce<number>((acc, curr) => acc + curr, 0)
);
const minorIntervals = [0, 2, 1, 2, 2, 1, 2];
const minorIntervalsFromRoot = minorIntervals.map((interval, idx) =>
  minorIntervals.slice(0, idx + 1).reduce<number>((acc, curr) => acc + curr, 0)
);

const getNotesOfScale = (intervals: number[], root: string) =>
  intervals.reduce<string[]>((acc, curr) => {
    const index = notes.findIndex((elem) => elem === root) + curr;
    const noteIndex = index >= 12 ? index - 12 : index;
    acc.push(notes[noteIndex]);
    return acc;
  }, []);

const majorScales = notes
  .map((note) => {
    const notesOfScale = getNotesOfScale(majorIntervalsFromRoot, note);
    return {
      [note]: notesOfScale,
    };
  })
  .reduce((acc, curr) => Object.assign(acc, curr), {});

const minorScales = notes
  .map((note) => {
    const notesOfScale = getNotesOfScale(minorIntervalsFromRoot, note);
    return {
      [`${note}m`]: notesOfScale,
    };
  })
  .reduce((acc, curr) => Object.assign(acc, curr), {});

const scales = Object.assign(majorScales, minorScales);

// console.log(scales);

const notesToFind: string[] = Array.from(
  new Set(Deno.args.filter((arg) => notes.includes(arg)))
);

let candidates: string[] = [];

for (const scaleKey in scales) {
  if (notesToFind.every((curr) => scales[scaleKey].includes(curr))) {
    candidates.push(scaleKey);
  }
}

console.log({ candidates });