使用js2.点击登录按钮 弹框提示 “您已经在登录界面” 3.手机号文本框的验证 为失焦验证 4.验证手机号的长度为11位的数字 并且第一位必须为1 5.手机号验证失败 则清空手机号文本框所有内容 6.验证码为随机的四位英文 7.点击验证码进行随机切换 8.验证码验证失败 则清空验证码文本框的内容 9.验证码的验证不区分大小写 10.点击发送验证码 出现20s倒计时 按钮禁用 11.倒计时结束后 按钮禁用解除

好的，您的第一个问题是关于前端开发的，我可以帮您解答。针对您的需求，可以使用以下代码实现：

1. 点击登录按钮弹框提示 "您已经在登录界面"

const loginBtn = document.querySelector('#login-btn');
loginBtn.addEventListener('click', () => {
  alert('您已经在登录界面');
});

2. 手机号文本框的验证为失焦验证

const phoneInput = document.querySelector('#phone-input');
phoneInput.addEventListener('blur', () => {
  // 手机号验证逻辑
});

3. 验证手机号的长度为11位的数字，并且第一位必须为1

const phoneInput = document.querySelector('#phone-input');
phoneInput.addEventListener('blur', () => {
  const phone = phoneInput.value;
  const reg = /^1\d{10}$/;
  if (!reg.test(phone)) {
    phoneInput.value = '';
    alert('请输入11位数字手机号，第一位必须为1');
  }
});

4. 手机号验证失败则清空手机号文本框所有内容

const phoneInput = document.querySelector('#phone-input');
phoneInput.addEventListener('blur', () => {
  const phone = phoneInput.value;
  const reg = /^1\d{10}$/;
  if (!reg.test(phone)) {
    phoneInput.value = '';
    alert('请输入11位数字手机号，第一位必须为1');
  }
});

5. 验证码为随机的四位英文

const codeBtn = document.querySelector('#code-btn');
const codeInput = document.querySelector('#code-input');
const codes = ['ABCD', 'EFGH', 'IJKL', 'MNOP'];
codeBtn.addEventListener('click', () => {
  const code = codes[Math.floor(Math.random() * codes.length)];
  codeBtn.textContent = code;
});

6. 点击验证码进行随机切换

const codeBtn = document.querySelector('#code-btn');
const codeInput = document.querySelector('#code-input');
const codes = ['ABCD', 'EFGH', 'IJKL', 'MNOP'];
codeBtn.addEventListener('click', () => {
  const code = codes[Math.floor(Math.random() * codes.length)];
  codeBtn.textContent = code;
});

7. 验证码验证失败则清空验证码文本框的内容，并弹出提示

const codeBtn = document.querySelector('#code-btn');
const codeInput = document.querySelector('#code-input');
const codes = ['ABCD', 'EFGH', 'IJKL', 'MNOP'];
codeBtn.addEventListener('click', () => {
  const code = codes[Math.floor(Math.random() * codes.length)];
  codeBtn.textContent = code;
});

codeInput.addEventListener('blur', () => {
  const inputCode = codeInput.value;
  const code = codeBtn.textContent;
  if (inputCode.toLowerCase() !== code.toLowerCase()) {
    codeInput.value = '';
    alert('验证码错误，请重新输入');
  }
});

8. 点击发送验证码出现20s倒计时，按钮禁用

const codeBtn = document.querySelector('#code-btn');
const codeInput = document.querySelector('#code-input');
const codes = ['ABCD', 'EFGH', 'IJKL', 'MNOP'];
let count = 20;
let timer = null;
codeBtn.addEventListener('click', () => {
  const code = codes[Math.floor(Math.random() * codes.length)];
  codeBtn.textContent = code;
  codeBtn.disabled = true;
  timer = setInterval(() => {
    count--;
    if (count === 0) {
      clearInterval(timer);
      codeBtn.disabled = false;
      codeBtn.textContent = '发送验证码';
      count = 20;
    } else {
      codeBtn.textContent = `${count}s后重新发送`;
    }
  }, 1000);
});

codeInput.addEventListener('blur', () => {
  const inputCode = codeInput.value;
  const code = codeBtn.textContent;
  if (inputCode.toLowerCase() !== code.toLowerCase()) {
    codeInput.value = '';
    alert('验证码错误，请重新输入');
  }
});

9. 验证码的验证不区分大小写

const codeBtn = document.querySelector('#code-btn');
const codeInput = document.querySelector('#code-input');
const codes = ['ABCD', 'EFGH', 'IJKL', 'MNOP'];
let count = 20;
let timer = null;
codeBtn.addEventListener('click', () => {
  const code = codes[Math.floor(Math.random() * codes.length)];
  codeBtn.textContent = code;
  codeBtn.disabled = true;
  timer = setInterval(() => {
    count--;
    if (count === 0) {
      clearInterval(timer);
      codeBtn.disabled = false;
      codeBtn.textContent = '发送验证码';
      count = 20;
    } else {
      codeBtn.textContent = `${count}s后重新发送`;
    }
  }, 1000);
});

codeInput.addEventListener('blur', () => {
  const inputCode = codeInput.value;
  const code = codeBtn.textContent;
  if (inputCode.toLowerCase() !== code.toLowerCase()) {
    codeInput.value = '';
    alert('验证码错误，请重新输入');
  }
});

10. 倒计时结束后，按钮禁用解除

const codeBtn = document.querySelector('#code-btn');
const codeInput = document.querySelector('#code-input');
const codes = ['ABCD', 'EFGH', 'IJKL', 'MNOP'];
let count = 20;
let timer = null;
codeBtn.addEventListener('click', () => {
  const code = codes[Math.floor(Math.random() * codes.length)];
  codeBtn.textContent = code;
  codeBtn.disabled = true;
  timer = setInterval(() => {
    count--;
    if (count === 0) {
      clearInterval(timer);
      codeBtn.disabled = false;
      codeBtn.textContent = '发送验证码';
      count = 20;
    } else {
      codeBtn.textContent = `${count}s后重新发送`;
    }
  }, 1000);
});

codeInput.addEventListener('blur', () => {
  const inputCode = codeInput.value;
  const code = codeBtn.textContent;
  if (inputCode.toLowerCase() !== code.toLowerCase()) {
    codeInput.value = '';
    alert('验证码错误，请重新输入');
  }
});

以上代码可以实现您所需的功能，您可以根据自己的需求进行修改。