arp-style.js

module.exports = {
  "Up": [ 0, 1, 2, 3 ],
  "Down": [ 3, 2, 1, 0 ],
  "UpDown": [ 0, 1, 2, 3, 2, 1 ],
  "DownUp": [ 3, 2, 1, 0, 1, 2 ],
  "Down&Up": [ 3, 2, 1, 0, 0, 1, 2, 3 ],
  "Up&Down": [ 0, 1, 2, 3, 3, 2, 1, 0 ],
  "Converge": [ 0, 3, 1, 2 ],
  "Diverge": [ 2, 1, 3, 0 ],
  "Con&Diverge": [ 0, 3, 1, 2, 1, 3 ],
  "PinkyUp": [ 0, 3, 1, 3, 2, 3 ],
  "PinkyUpDown": [ 0, 3, 1, 3, 2, 3, 1, 3 ],
  "ThumbUp": [ 0, 1, 0, 2, 0, 3 ],
  "ThumbUpDown": [ 0, 1, 0, 2, 0, 3, 0, 2 ]
};

arp.js

"use strict";

function up(list) {
  return toArray(list).sort(asc);
}

function down(list) {
  return toArray(list).sort(desc);
}

function upDown(list) {
  list = toArray(list).sort(asc);
  return list.concat(list.slice(1, -1).reverse());
}

function downUp(list) {
  list = toArray(list).sort(desc);
  return list.concat(list.slice(1, -1).reverse());
}

function upAndDown(list) {
  list = toArray(list).sort(asc);
  return list.concat(list.slice().reverse());
}

function downAndUp(list) {
  list = toArray(list).sort(desc);
  return list.concat(list.slice().reverse());
}

function converge(list) {
  var result = [];
  list = toArray(list).sort(asc);
  while (list.length) {
    result.push(list.shift());
    if (list.length) {
      result.push(list.pop());
    }
  }
  return result;
}

function diverge(list) {
  return converge(list).reverse();
}

function conAndDiverge(list) {
  list = converge(list);
  return list.concat(list.slice(1, -1).reverse());
}

function pinkyUp(list) {
  list = toArray(list).sort(asc);
  var x = list.pop();
  return list.reduce((a, b) => a.concat(b, x), []);
}

function pinkyUpDown(list) {
  list = toArray(list).sort(asc);
  var x = list.pop();
  list = list.concat(list.slice(1, -1).reverse());
  return list.reduce((a, b) => a.concat(b, x), []);
}

function thumbUp(list) {
  list = toArray(list).sort(asc);
  var x = list.shift();
  return list.reduce((a, b) => a.concat(x, b), []);
}

function thumbUpDown(list) {
  list = toArray(list).sort(asc);
  var x = list.shift();
  list = list.concat(list.slice(1, -1).reverse());
  return list.reduce((a, b) => a.concat(x, b), []);
}

function toArray(list) {
  return Array.prototype.slice.call(list);
}

function asc(a, b) {
  return a - b;
}

function desc(a, b) {
  return b - a;
}

module.exports = {
  "Up": up,
  "Down": down,
  "UpDown": upDown,
  "DownUp": downUp,
  "Up & Down": upAndDown,
  "Down & Up": downAndUp,
  "Converge": converge,
  "Diverge": diverge,
  "Con & Diverge": conAndDiverge,
  "Pinky Up": pinkyUp,
  "Pinky UpDown": pinkyUpDown,
  "Thumb Up": thumbUp,
  "Thumb UpDown": thumbUpDown
};

var arp = module.exports;
var chord = [ 0, 2, 1, 3, 4, 5 ];

for (let name in arp) {
  console.log(name, arp[name](chord))
}