modes.js

var globals = {
	naturals:    ['C', 'D', 'E', 'F', 'G', 'A', 'B'],
	degrees:     ['R', 'm2', 'M2', 'm3', 'M3', 'P4', ['A4', 'D5'], 'P5', 'm6', 'M6', 'm7', 'M7'],
	modeNames:   ['Ionian', 'Dorian', 'Phrygian', 'Lydian', 'Mixolydian', 'Aeolian', 'Locrian'],
	accidentals: {'-1': '♭', 0: '', 1: '♯'},
	scales: {
		'Major':               [2, 2, 1, 2, 2, 2, 1],
		'Minor':               [2, 1, 2, 2, 1, 2, 2],
		'Harmonic Minor':      [2, 1, 2, 2, 1, 3, 1],
		'Diminished Arpeggio': [3, 3, 3, 3]
	}
};


function modulate(arr, offset, alg) {
	if(! Array.isArray(arr) && ! Array.isArray(alg) && ! Number.isInteger(offset)) {
		return false;
	}
	var count = arr.length,
	    height = arr.length,
	    result = [];
	if(alg !== undefined) {
		result.push(arr[offset]);
		count = alg.length;
	}
	for(var i = 0, j = 0; i < count; ++i) {
		var node = offset + (alg ? j += alg[i] : i);
		if(node >= height)
			node %= height;
		var piece = arr[node];
		result.push(piece);
	}
	return result;
}

function addAccidentals(notes, scale) {
	// ????
}

console.log('major degrees:', modulate(globals.degrees, 0, globals.scales.Minor));
var naturals = ['C', 'D', 'E', 'F', 'G', 'A', 'B'];
for (var i=0; i < naturals.length; ++i) {
	var scale = 'Major';
	var key = naturals[i];
	console.log(key + ' ' +scale, modulate(globals.naturals, globals.naturals.indexOf(key)));
}
console.log('minor degrees:',modulate(globals.degrees, 0, globals.scales.Minor));
for (var i=0; i < naturals.length; ++i) {
	var scale = 'Minor';
	var key = naturals[i];
	console.log(key + ' ' + scale.toLowerCase(), modulate(globals.naturals, globals.naturals.indexOf(key)));
}