还有另一个版本，清晰而简单，处理移位的capsLock，并且不受ascii限制，我认为:

document.onkeypress = function (e)
{
    e = e || window.event;
    if (e.charCode === 0 || e.ctrlKey || document.onkeypress.punctuation.indexOf(e.charCode) >= 0)
        return;
    var s = String.fromCharCode(e.charCode); // or e.keyCode for compatibility, but then have to handle MORE non-character keys
    var s2 = e.shiftKey ? s.toUpperCase() : s.toLowerCase();
    var capsLockOn = (s2 !== s);
    document.getElementById('capslockWarning').style.display = capsLockOn ? '' : 'none';
}
document.onkeypress.punctuation = [33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,91,92,93,94,95,96,123,124,125,126];

编辑:意义上的capsLockOn被逆转，多，固定。

编辑#2:在进一步检查之后，我做了一些更改，不幸的是，代码更详细了一些，但它可以适当地处理更多的操作。

Using e.charCode instead of e.keyCode and checking for 0 values skips a lot of non-character keypresses, without coding anything specific to a given language or charset. From my understanding, it's slightly less compatible, so older, non-mainstream, or mobile browsers may not behave as this code expects, but it's worth it, for my situation anyway. Checking against a list of known punctuation codes prevents them from being seen as false negatives, since they're not affected by caps lock. Without this, the caps lock indicator gets hidden when you type any of those punctuation characters. By specifying an excluded set, rather than an included one, it should be more compatible with extended characters. This is the ugliest, special-casiest bit, and there's some chance that non-Western languages have different enough punctuation and/or punctuation codes to be a problem, but again it's worth it IMO, at least for my situation.

上面莫蒂和迭戈·维埃拉的回答是我们最终使用的，现在应该是公认的答案。然而，在我注意到它之前，我写了这个不依赖字符代码的小javascript函数……

var capsLockIsOnKeyDown = {shiftWasDownDuringLastChar: false,
  capsLockIsOnKeyDown: function(event) {
    var eventWasShiftKeyDown = event.which === 16;
    var capsLockIsOn = false;
    var shifton = false;
    if (event.shiftKey) {
        shifton = event.shiftKey;
    } else if (event.modifiers) {
        shifton = !!(event.modifiers & 4);
    }

    if (event.target.value.length > 0 && !eventWasShiftKeyDown) {
      var lastChar = event.target.value[event.target.value.length-1];
      var isAlpha = /^[a-zA-Z]/.test(lastChar);

      if (isAlpha) {
        if (lastChar.toUpperCase() === lastChar && lastChar.toLowerCase() !== lastChar
          && !event.shiftKey && !capsLockIsOnKeyDown.shiftWasDownDuringLastChar) {
          capsLockIsOn =  true;
        }
      }
    }
    capsLockIsOnKeyDown.shiftWasDownDuringLastChar = shifton;
    return capsLockIsOn;
  }
}

然后在事件处理程序中调用比如capslockisonkeydown。capslockisonkeydown(事件)

但最后我们还是用了@ motie和@Diego Vieira的回应

jQuery:

$('some_element').keypress(function(e){
       if(e.keyCode == 20){
             //caps lock was pressed
       }
});

这个jQuery插件(代码)实现了与Rajesh的回答相同的想法，更简洁一点。

最近在hashcode.com上有一个类似的问题，我创建了一个jQuery插件来处理它。它还支持对数字的大写锁定识别。(在标准德语键盘布局上，大写锁定对数字有影响)。

你可以在这里查看最新版本:jquery.capsChecker

有一个更简单的检测caps-lock的解决方案:

function isCapsLockOn(event) {
    var s = String.fromCharCode(event.which);
    if (s.toUpperCase() === s && s.toLowerCase() !== s && !event.shiftKey) {
        return true;
    }
}

我写了一个名为capsLock的库，它完全是你想要它做的。

只要把它包括在你的网页上:

<script src="https://rawgit.com/aaditmshah/capsLock/master/capsLock.js"></script>

然后像这样使用它:

alert(capsLock.status);

capsLock.observe(function (status) {
    alert(status);
});

参见演示:http://jsfiddle.net/3EXMd/

按下“Caps Lock”键更新状态。它只使用Shift键来确定Caps Lock键的正确状态。最初状态为false。所以要小心。