Note to Midi Number

getMidiNumber.js

/**
 * Get the midi note number of a note string
 * 
 * @param {string} note
 * 
 * @returns {number} MIDI note number
 */
function getMidiNumber(note) {

    // Based on 1st octave of each note
    const NoteBaseNumbers = {
        a: 33,
        b: 35,
        c: 24,
        d: 26,
        e: 28,
        f: 29,
        g: 31
    }

    let noteParts = [...note.toLowerCase()]

    let letter = noteParts[0]
    let octave = parseInt(noteParts[noteParts.length - 1])
    let accidental = noteParts.length > 2 ? noteParts[1] : false

    if (!Object.keys(NoteBaseNumbers).includes(letter)) {
        throw `That note does not exist.`
    }

    if (noteParts.length > 3) {
        throw `MIDI don't go that high!`
    }

    /**
     * CALCULATIONS
     */
    let octaveModifier = (octave - 1) * 12
    
    let baseValue = NoteBaseNumbers[letter]

    let value = baseValue + octaveModifier

    if (accidental && accidental === 'b') {
        value--
    } 

    if (accidental && accidental === '#') {
        value++
    } 

    // Lowest note is A0 with value of 21
    if (value < 21) {
        throw `That note does not exist.`
    }

    return value
}