scales.js

let base = localStorage.getItem('baseNote');
let text = document.createElement("p");
let node = document.createTextNode("Your base note was " + base + ".");
text.append(node);
body.insertBefore(text, body.childNodes[3]);

let upNotes = ["A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#"];
let downNotes = ["G#", "G", "F#", "F", "E", "D#", "D", "C#", "C", "B", "A#", "A"];
let baseIndex;
if (fileName[0] == "second-step.html") {
  baseIndex = upNotes.findIndex(element => {
      return element === base.substring(0, base.length - 1);
      });
} else {
  baseIndex = downNotes.findIndex(element => {
      return element == base.substring(0, base.length - 1);
      });
}

let i = 1;
let octaveNumber = base.charAt(base.length -1);
let prevOctave = octaveNumber;
let note = base.substring(0, base.length - 1);
let prevNote = note;

function nextNote() {
  prevNote = note;
  if (fileName[0] == "second-step.html") {
    note = upNotes[(baseIndex + i) % 12];
    if (note === "C") {
      octaveNumber++;
    } else if (note === "C#") {
      prevOctave = octaveNumber;
    }
  } else {
    note = downNotes[(baseIndex + i) % 12];
    if (note === "B") {
      octaveNumber--;
    } else if (note === "A#") {
      prevOctave = octaveNumber;
    }
  }
  let singText = document.createElement("p");
  let sing = document.createTextNode("Now, try to sing " + note + octaveNumber + ".");
  singText.append(sing);
  singText.setAttribute("id", "noteToSing");
  body.insertBefore(singText, body.childNodes[4]);
  i++;
}
nextNote();

function pass() {
  let noteToSing = document.getElementById("noteToSing");
  if (noteToSing != null) {
    noteToSing.parentNode.removeChild(noteToSing);
  }
  nextNote();
}

function fail() {
  let next = document.createElement("BUTTON");
  next.innerHTML = "Next Step";

  let text = document.createElement("p");
  let node;

  if (fileName[0] === "second-step.html") {
    localStorage.setItem('highNote', prevNote + prevOctave);
    next.setAttribute("onclick", "location.href = 'third-step.html'");
    node = document.createTextNode("Your highest note is " + prevNote + prevOctave + ".");
  } else {
    localStorage.setItem('lowNote', prevNote + prevOctave);
    next.setAttribute("onclick", "location.href = 'results.html'");
    node = document.createTextNode("Your lowest note is " + prevNote + prevOctave + ".");
  }

  text.append(node);

  let tryagain = document.createElement("BUTTON");
  tryagain.innerHTML = "Try Again";
  tryagain.onclick = function() {
    tryagain.parentNode.removeChild(tryagain);
    if (next != null) {
      next.parentNode.removeChild(next);
    }
    if (text != null) {
      text.parentNode.removeChild(text);
    }
    recordbutton.disabled = false;
  }

  let div = document.createElement("div");
  div.setAttribute("class", "divider");

  body.append(text);
  body.append(tryagain);
  body.append(div);
  body.append(next);

  recordbutton.disabled = true;
}