<script> var timer = null; var ms = 0, s = 0, m = 0; var msElement = document.getElementById('ms'); var sElement = document.getElementById('s'); var mElement = document.getElementById('m'); var startButton = document.getElementById('start'); var pauseButton = document.getElementById('pause'); var resetButton = document.getElementById('reset'); 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'; }; </script> 补全JS代码实现：初始化:暂停-复位按钮失效;复位后,暂停按钮失效

可以在复位按钮的点击事件中添加一个判断，如果当前定时器不为null，则暂停按钮失效，代码如下：

resetButton.onclick = function() { 
    clearInterval(timer); 
    timer = null; 
    ms = 0; 
    s = 0; 
    m = 0; 
    msElement.innerText = '00'; 
    sElement.innerText = '00'; 
    mElement.innerText = '00'; 
    pauseButton.disabled = true; // 暂停按钮失效
    if (timer == null) {
        startButton.disabled = false; // 启动按钮生效
    }
};

在启动按钮的点击事件中添加一个判断，如果当前定时器为null，则启动按钮失效，代码如下：

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); 
    } 
    startButton.disabled = true; // 启动按钮失效
    pauseButton.disabled = false; // 暂停按钮生效
};