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var sharpChords = ['C', 'C♯', 'D', "D♯", 'E', 'F', "F♯", 'G', 'G♯', 'A', 'A♯', 'B'];
var flatChords = ['C', 'D♭', 'D', 'E♭', 'E', 'F', 'G♭', 'G', 'A♭', 'A', 'B♭', 'B'];
var sharpChordsFree = ['C', 'C#', 'D', "D#", 'E', 'F', "F#", 'G', 'G#', 'A', 'A#', 'B'];
var flatChordsFree = ['C', 'Db', 'D', 'Eb', 'E', 'F', 'Gb', 'G', 'Ab', 'A', 'Bb', 'B'];
function transposeChordName(chord, steps, preferFlats, freeGCchord) {
if (!steps || (steps % 12 === 0)) // The chords are the same if it is an exact octave change.
return chord;
// There are two things in the chord that might need to be transposed:
// The chord will start with a letter from A-G, and might have one accidental after it.
// That accidental might be an actual sharp or flat char, or it might be a pound sign or lower case "b".
// Then there is a bunch of stuff that isn't transposed and should just be copied. That is stuff like "7" and more complicated chords.
// But there is one other exception: right after a slash there will be a bass note and possibly an accidental. That should also be transposed.
while (steps < 0) steps += 12;
if (steps > 11) steps = steps % 12;
// (chord name w/accidental) (a bunch of stuff) (/) (bass note) (anything else)
var match = chord.match(/^([A-G][b#♭♯]?)([^\/]+)?\/?([A-G][b#♭♯]?)?(.+)?/)
if (!match)
return chord; // We don't recognize the format of the chord, so skip it.
var name = match[1]
var extra1 = match[2]
var bass = match[3]
var extra2 = match[4]
var index = sharpChords.indexOf(name)
if (index < 0)
index = flatChords.indexOf(name)
if (index < 0)
index = sharpChordsFree.indexOf(name)
if (index < 0)
index = flatChordsFree.indexOf(name)
if (index < 0)
return chord; // This should never happen, but if we can't find the chord just bail.
index += steps
index = index % 12
if (preferFlats) {
if (freeGCchord) chord = flatChordsFree[index]
else chord = flatChords[index]
} else {
if (freeGCchord) chord = sharpChordsFree[index]
else chord = sharpChords[index]
}
if (extra1)
chord += extra1
if (bass) {
var index = sharpChords.indexOf(bass)
if (index < 0)
index = flatChords.indexOf(bass)
if (index < 0)
index = sharpChordsFree.indexOf(bass)
if (index < 0)
index = flatChordsFree.indexOf(bass)
chord += '/'
if (index >= 0) {
index += steps
index = index % 12
if (preferFlats) {
if (freeGCchord) chord += flatChordsFree[index]
else chord += flatChords[index]
} else {
if (freeGCchord) chord += sharpChordsFree[index]
else chord += sharpChords[index]
}
} else
chord += bass; // Don't know what to do so do nothing
}
if (extra2)
chord += extra2
return chord;
}
module.exports = transposeChordName |