Javascript/四択クイズ

var radio0 = document.getElementById("radio0");
var radio1 = document.getElementById("radio1");
var radio2 = document.getElementById("radio2");
var radio3 = document.getElementById("radio3");
var question = document.getElementById("question");
var greeting = document.getElementById("greeting");
var startNext = document.getElementById("startNext");

var qas = [
	{question: "question01",
		ans0: "ans0", ans1: "ans1", ans2: "ans2", ans3: "ans3", answer: 0},
	{question: "question02",
		ans0: "ans0", ans1: "ans1", ans2: "ans2", ans3: "ans3", answer: 1},
	{question: "question03",
		ans0: "ans0", ans1: "ans1", ans2: "ans2", ans3: "ans3", answer: 2},
	{question: "question04",
		ans0: "ans0", ans1: "ans1", ans2: "ans2", ans3: "ans3", answer: 3}
];

var counter = -1;
var success = 0;

function nextquestion(){
  var qa = qas[counter];
  question.innerHTML = (counter + 1) + "." + qa.question;
  freeAllRadioButtons();
  radio0.nextElementSibling.innerHTML = "1." + qa.ans0;
  radio1.nextElementSibling.innerHTML = "2." + qa.ans1;
  radio2.nextElementSibling.innerHTML = "3." + qa.ans2;
  radio3.nextElementSibling.innerHTML = "4." + qa.ans3;
  greeting.innerHTML = "";
  hideElement(startNext, true);
}
function checkZero(){judge(0);}
function checkOne(){judge(1);}
function checkTwo(){judge(2);}
function checkThree(){judge(3);}

function runQuiz(){
  var quizform = document.getElementById("quizform");
  if(counter == -1){
  	hideElement(quizform, false);
  	greeting.innerHTML = "";
  }
  if(counter < qas.length - 1){
  	nextquestion(++counter);
  } else {
  	hideElement(quizform, true);
  	hideElement(startNext, true);
  	greeting.innerHTML = "正解率は" + success + "/" + qas.length;
  	greeting.nextElementSibling.innerHTML = "";
  }
}

function judge(selected){
  var rightAnswer = (qas[counter]).answer;
  if(selected == rightAnswer){
  	greeting.innerHTML = "○";
  	success++;
  } else {
  	greeting.innerHTML = "×　正解は" + (rightAnswer + 1);
  }
  greeting.nextElementSibling.innerHTML = "正解" + success + "/" + qas.length;
  hideElement(startNext, false);
  startNext.innerHTML = "next";
  disabledAllRadioButtons(true);
}
function hideElement(elm, b){
  if(b == true){
  	elm.style.display = "none";
  } else {
  	elm.style.display = "inline";
  }
}
function disabledAllRadioButtons(b){
  radio0.disabled = b;
  radio1.disabled = b;
  radio2.disabled = b;
  radio3.disabled = b;
}
function freeAllRadioButtons(){
  radio0.checked = false;
  radio1.checked = false;
  radio2.checked = false;
  radio3.checked = false;
  disabledAllRadioButtons(false);
}