determine if a set of notes can be physically fretted on guitar
npm install frettable --saveFrettable takes an array of notes, each representing the fret on a standard 6-string guitar.
An open note is represented as 0, and a muted note as -1. An open D chord would look like [-1, -1, 0, 2, 3, 2]
Based on the possible fingerings, frettable will determine whether or not the chord is "frettable."
const frettable = require('frettable');
let chord;
chord = [-1, -1, 0, 2, 3, 2]; // D chord
console.log(frettable(chord)); // true
chord = [1, 2, 3, 4, 5, 6];
console.log(frettable(chord)); // false - this chord is impossible to fret