Chord Progression Generator

progression_generator.js

// you can run this at https://jsbin.com/lohoval/7/edit?js,console

var progression = function(){
    var currentKey = "";
    var chords = {
        "A"     : ["A", "Bmin", "C#min", "D", "E", "F#min", "G#°"],
        "B"     : ["B", "C#min", "D#min", "E", "F", "G#min", "A#°"],
        "C"     : ["C", "Dmin", "Emin", "F", "G", "Amin", "B°"],
        "D"     : ["D", "Emin", "F#min", "G", "A", "Bmin", "C#°"],
        "E"     : ["E", "F#min", "G#min", "A", "B", "C#min", "D#°"],
        "F"     : ["F", "Gmin", "Amin", "Bb", "C", "Dmin", "E°"],
        "G"     : ["G", "Amin", "Bmin", "C", "D", "Emin", "F#°"],
        "Amin"  : ["Amin", "B°", "C", "Dmin", "Emin", "F", "G"],
        "Bmin"  : ["Bmin", "C#°", "D", "Emin", "F#min", "G", "A"],
        "Cmin"  : ["Cmin", "D°", "Eb", "Fmin", "Gmin", "Ab", "Bb"],
        "Dmin"  : ["Dmin", "E°", "F", "Gmin", "Amin", "Bb", "C"],
        "Emin"  : ["Emin", "F#°", "G", "Amin", "Bmin", "C", "D"],
        "Fmin"  : ["Fmin", "G°", "Abmin", "Bbmin", "Cmin", "Db", "Eb"],
        "Gmin"  : ["Gmin", "A°", "Bb", "Cmin", "Dmin", "Eb", "F"]
    };

    return {
        getNumber : function(){
            return Math.floor(Math.random() * chords[this.currentKey].length) + 1  
        },
        generate : function (thisKey){
            this.currentKey = thisKey;
            var degrees = [1,this.getNumber(),this.getNumber(),this.getNumber()];
            degrees.forEach(element => {
                console.log(chords[this.currentKey][element-1]);
            })
            var baseURL = "https://www.songtive.com/en/chords/guitar/standard/";
            console.log("Full chord charts at " + baseURL + this.currentKey);
        }        
    }
}();

// ##### LOOK HERE.  JUST CHANGE THE KEY
// FOR A MAJOR use 'A', FOR A MINOR use 'Amin'

progression.generate('C');

Sample output for key of C:

C
Dmin
B°
G
Full chord charts at https://www.songtive.com/en/chords/guitar/standard/C