validate-note/src/index.js

🎼 Validates a note (scientific pitch notation) and throws errors if needed

// @flow

import convertFlatToSharp from './lib/convertFlatToSharp';

type options = {
  maxOctave: number,
  flatToSharp: boolean,
  octave: boolean
};

const isSignature = value => (value === `b` || value === `#`);
const isOctave = value => !Number.isNaN(value);

export default (note: string, {
  maxOctave = 8,
  flatToSharp = false,
  octave: rOct = false
}: options = {}): Object => {

  const oct = rOct ? `1` : `0,1`;

  const regex = new RegExp(`^(?!([EB]#)|([CF]b))([A-G]{1})([#|b]{0,1})([0-${maxOctave}]{${oct}})$`, `ig`);

  if (!regex.test(note)) throw new Error(`'${note}' is not a valid note`);

  let letter: string = note.charAt(0);
  let signature: string = ``;
  let octave: number;

  for (let i = 1;i < note.length;i ++) {
    const part: any = note[i];
    if (isSignature(part)) signature = part;
    if (isOctave(part)) octave = parseInt(part);
  }

  if (signature === `b` && flatToSharp) {
    ({signature, letter} = convertFlatToSharp(letter, signature));
  }

  const obj = {
    letter,
    signature,
    octave
  };

  Object.keys(obj).forEach(key => (!obj[key]) && delete obj[key]);

  return obj;

};