Bagaimana untuk menaip kod pengesahan dalam javascript

//生成随机字符串
function createCode() {
  var code = "";
  var codeLength = 4; //验证码长度
  var charList = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
  for (var i = 0; i < codeLength; i++) {
    var randomCharIndex = Math.floor(Math.random() * charList.length);
    code += charList[randomCharIndex];
  }
  return code;
}

//设置背景颜色
function drawBackground(ctx) {
  ctx.fillStyle = "#eee"; //背景颜色
  ctx.fillRect(0, 0, 80, 28); //画出矩形背景
}

//画出随机字符串
function drawCode(ctx, code) {
  ctx.fillStyle = "#000"; //字符串颜色
  ctx.font = "24px Arial"; //字体大小和字体
  ctx.fillText(code, 10, 22); //绘制文字
}

//生成验证码
function createCheckCode() {
  var canvas = document.getElementById("checkCodeCanvas");
  var ctx = canvas.getContext("2d");
  drawBackground(ctx);
  var code = createCode();
  drawCode(ctx, code);
  return code; //将生成的验证码返回
}

//生成随机字符串
function createCode() {
  var code = "";
  var codeLength = 4; //验证码长度
  var charList = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
  for (var i = 0; i < codeLength; i++) {
    var randomCharIndex = Math.floor(Math.random() * charList.length);
    code += charList[randomCharIndex];
  }
  return code;
}

//生成验证码图片
function createCheckCode() {
  var code = createCode();
  var checkCodeImg = document.getElementById("checkCodeImg");
  checkCodeImg.src = "checkCode.php?code=" + code;
  return code; //将生成的验证码返回
}

function validateCheckCode() {
  var inputCode = document.getElementById("inputCode").value.trim().toLowerCase();
  var checkCode = document.getElementById("checkCode").value.toLowerCase(); //checkCode是之前生成的随机字符串
  if (inputCode.length <= 0) {
    alert("请输入验证码！");
    return false;
  } else if (inputCode != checkCode) {
    alert("验证码错误！请重新输入！");
    createCheckCode(); //生成新的验证码
    document.getElementById("inputCode").value = ""; //清空输入框
    return false;
  } else {
    alert("验证码正确！");
    return true;
  }
}