JS this关键字在ajax中使用出现问题解决方案

var clock = '';
  var nums = 60;
  var btn;
  function sendCode(thisBtn) {
    btn = thisBtn;
    btn.disabled = true; //将按钮置为不可点击
    btn.value = nums + '秒重新获取';
    btn.className = 'regGetcodeBtn1';
    if (clickNumber == 0) {
      clock = setInterval(doLoop, 1000); //一秒执行一次
    }
  }

function doLoop() {
    nums--;
    if (nums > 0) {
      btn.value = nums + '秒后重新获取';
      clickNumber = 1;
    } else {
      clearInterval(clock); //清除js定时器
      btn.disabled = false;
      btn.value = '获取验证码';
      btn.className = 'regGetcodeBtn1 color';
      nums = 60; //重置时间
      clickNumber = 0;
    }
  }

$.ajax({
      url: servletUrl,
      type: "post",
      dataType: 'JSON',
      data: { name: name, securityCode: txtsecurityCode1/* strTelphone: strCodeTelphone, securityCode: txtsecurityCode1*