Many existing answers will check for caps lock on when shift is not pressed but will not check for it if you press shift and get lowercase, or will check for that but will not also check for caps lock being off, or will check for that but will consider non-alpha keys as 'off'. Here is an adapted jQuery solution that will show a warning if an alpha key is pressed with caps (shift or no shift), will turn off the warning if an alpha key is pressed without caps, but will not turn the warning off or on when numbers or other keys are pressed.

$("#password").keypress(function(e) { 
    var s = String.fromCharCode( e.which );
    if ((s.toUpperCase() === s && s.toLowerCase() !== s && !e.shiftKey)|| //caps is on
      (s.toUpperCase() !== s && s.toLowerCase() === s && e.shiftKey)) {
        $("#CapsWarn").show();
    } else if ((s.toLowerCase() === s && s.toUpperCase() !== s && !e.shiftKey)||
      (s.toLowerCase() !== s && s.toUpperCase() === s && e.shiftKey)) { //caps is off
        $("#CapsWarn").hide();
    } //else upper and lower are both same (i.e. not alpha key - so do not hide message if already on but do not turn on if alpha keys not hit yet)
  });

你可以试试。增加了一个工作示例。当焦点在输入上时，打开caps lock使led变成红色或绿色。(还没有在mac/linux上测试)

注意:两个版本都适用于我。感谢您在评论中提出建设性意见。

旧版本:https://jsbin.com/mahenes/edit?js,output

另外，这是一个修改后的版本(有人能在mac上测试并确认吗)

新版本:https://jsbin.com/xiconuv/edit?js,output

新版本:

function isCapslock(e) {
  const IS_MAC = /Mac/.test(navigator.platform);

  const charCode = e.charCode;
  const shiftKey = e.shiftKey;

  if (charCode >= 97 && charCode <= 122) {
    capsLock = shiftKey;
  } else if (charCode >= 65 && charCode <= 90
    && !(shiftKey && IS_MAC)) {
    capsLock = !shiftKey;
  }

  return capsLock;
}

旧版本:

function isCapslock(e) {
  e = (e) ? e : window.event;

  var charCode = false;
  if (e.which) {
    charCode = e.which;
  } else if (e.keyCode) {
    charCode = e.keyCode;
  }

  var shifton = false;
  if (e.shiftKey) {
    shifton = e.shiftKey;
  } else if (e.modifiers) {
    shifton = !!(e.modifiers & 4);
  }

  if (charCode >= 97 && charCode <= 122 && shifton) {
    return true;
  }

  if (charCode >= 65 && charCode <= 90 && !shifton) {
    return true;
  }

  return false;
}

对于国际字符，可以根据需要为以下键添加额外的检查。你必须获得你感兴趣的字符的键码范围，可能是通过使用一个键映射数组，它将保存你正在寻址的所有有效用例键…

大写字母A-Z或'Ä'， 'Ö'， 'Ü'， 小写字母a-Z或0-9或'ä'， 'ö'， 'ü'

上面的键只是示例表示。

当您键入时，如果caplock是打开的，它可以自动将当前字符转换为小写字母。这样，即使打开了caplocks，它的行为也不会像在当前页面上那样。为了通知您的用户，您可以显示一个文本，说明caplocks已打开，但表单条目已转换。

Javascript代码

<script type="text/javascript">
   function isCapLockOn(e){
   kc = e.keyCode?e.keyCode:e.which;
   sk = e.shiftKey?e.shiftKey:((kc == 16)?true:false);
   if(((kc >= 65 && kc <= 90) && !sk)||((kc >= 97 && kc <= 122) && sk))
       document.getElementById('alert').style.visibility = 'visible';
   else
       document.getElementById('alert').style.visibility = 'hidden';
   }
</script>

现在我们需要使用Html来关联这个脚本

<input type="password" name="txtPassword" onkeypress="isCapLockOn(event)" />
<div id="alert" style="visibility:hidden">Caps Lock is on.</div> 

We use getModifierState to check for caps lock, it's only a member of a mouse or keyboard event so we cannot use an onfocus. The most common two ways that the password field will gain focus is with a click in or a tab. We use onclick to check for a mouse click within the input, and we use onkeyup to detect a tab from the previous input field. If the password field is the only field on the page and is auto-focused then the event will not happen until the first key is released, which is ok but not ideal, you really want caps lock tool tips to display once the password field gains focus, but for most cases this solution works like a charm.

HTML

<input type="password" id="password" onclick="checkCapsLock(event)" onkeyup="checkCapsLock(event)" />

JS

function checkCapsLock(e) {
  if (e.getModifierState("CapsLock")) {
    console.log("Caps");
  }
}

https://codepen.io/anon/pen/KxJwjq

这是一个自定义的jquery插件，使用jquery ui，由这个页面上的所有好主意和工具提示小部件组成。大写锁定消息是自动应用于所有密码框，不需要更改您当前的html。

自定义插件代码…

(function ($) {
    $.fn.capsLockAlert = function () {
        return this.each(function () {
            var capsLockOn = false;
            var t = $(this);
            var updateStatus = function () {
                if (capsLockOn) {
                    t.tooltip('open');
                } else {
                    t.tooltip('close');
                }
            }
            t.tooltip({
                items: "input",
                position: { my: "left top", at: "left bottom+10" },
                open: function (event, ui) {
                    ui.tooltip.css({ "min-width": "100px", "white-space": "nowrap" }).addClass('ui-state-error');
                    if (!capsLockOn) t.tooltip('close');
                },
                content: function () {
                    return $('<p style="white-space: nowrap;"/>')
                        .append($('<span class="ui-icon ui-icon-alert" style="display: inline-block; margin-right: 5px; vertical-align: text-top;" />'))
                        .append('Caps Lock On');
                }
            })
            .off("mouseover mouseout")
            .keydown(function (e) {
                if (e.keyCode !== 20) return;
                capsLockOn = !capsLockOn;
                updateStatus();
            })
            .keypress(function (e) {
                var kc = e.which; //get keycode

                var isUp = (kc >= 65 && kc <= 90) ? true : false; // uppercase
                var isLow = (kc >= 97 && kc <= 122) ? true : false; // lowercase
                if (!isUp && !isLow) return; //This isn't a character effected by caps lock

                // event.shiftKey does not seem to be normalized by jQuery(?) for IE8-
                var isShift = (e.shiftKey) ? e.shiftKey : ((kc === 16) ? true : false); // shift is pressed

                // uppercase w/out shift or lowercase with shift == caps lock
                if ((isUp && !isShift) || (isLow && isShift)) {
                    capsLockOn = true;
                } else {
                    capsLockOn = false;
                }
                updateStatus();
            });
        });
    };
})(jQuery);

适用于所有密码元素…

$(function () {
    $(":password").capsLockAlert();
});