startButton.onclick = function() { if (timer == null) { timer = setInterval(function() { ms++; if (ms == 100) { ms = 0; s++; if (s == 60) { s = 0; m++; if (m == 60) { m = 0; } mElement.innerText = m < 10 ? '0' + m : m; } sElement.innerText = s < 10 ? '0' + s : s; } msElement.innerText = ms < 10 ? '0' + ms : ms; }, 10); } }; pauseButton.onclick = function() { clearInterval(timer); timer = null; }; resetButton.onclick = function() { clearInterval(timer); timer = null; ms = 0; s = 0; m = 0; msElement.innerText = '00'; sElement.innerText = '00'; mElement.innerText = '00'; };更改代码实现,初始化暂停和复位按钮失效(变灰),开始按钮触发后,暂停和复位按钮生效;复位后,暂停和复位按钮失效

可以通过设置按钮的 `disabled` 属性来实现按钮的禁用和启用。具体更改后的代码如下：

const startButton = document.getElementById('start');
const pauseButton = document.getElementById('pause');
const resetButton = document.getElementById('reset');
const msElement = document.getElementById('ms');
const sElement = document.getElementById('s');
const mElement = document.getElementById('m');

let ms = 0;
let s = 0;
let m = 0;
let timer = null;

startButton.onclick = function() {
  startButton.disabled = true;
  pauseButton.disabled = false;
  resetButton.disabled = false;
  
  if (timer == null) {
    timer = setInterval(function() {
      ms++;
      if (ms == 100) {
        ms = 0;
        s++;
        if (s == 60) {
          s = 0;
          m++;
          if (m == 60) {
            m = 0;
          }
          mElement.innerText = m < 10 ? '0' + m : m;
        }
        sElement.innerText = s < 10 ? '0' + s : s;
      }
      msElement.innerText = ms < 10 ? '0' + ms : ms;
    }, 10);
  }
};

pauseButton.onclick = function() {
  startButton.disabled = false;
  pauseButton.disabled = true;
  resetButton.disabled = false;
  
  clearInterval(timer);
  timer = null;
};

resetButton.onclick = function() {
  startButton.disabled = false;
  pauseButton.disabled = true;
  resetButton.disabled = true;
  
  clearInterval(timer);
  timer = null;
  ms = 0;
  s = 0;
  m = 0;
  msElement.innerText = '00';
  sElement.innerText = '00';
  mElement.innerText = '00';
};