<h1>检测大写锁定键</h1>
<form action="#" method="post">
    <p>
        <label for="password">密码：</label>
        <input type="password" id="password" name="password" /><span style="display:none;">大写锁定键被按下，请注意大小写</span>
    </p>
</form>
 
function  detectCapsLock(event){
	var e = event||window.event;
	var o = e.target||e.srcElement;
	var oTip = o.nextSibling;
    var keyCode  =  e.keyCode||e.which; // 按键的keyCode 
    var isShift  =  e.shiftKey ||(keyCode  ==   16 ) || false ; // shift键是否按住
    
    if (
        ((keyCode >=   65   &&  keyCode  <=   90 )  &&   !isShift)    // Caps Lock 打开，且没有按住shift键 
        || ((keyCode >=   97   &&  keyCode  <=   122 )  &&  isShift)    // Caps Lock 打开，且按住shift键
	 ) {
        oTip.style.display = '';
    } else {
        oTip.style.display  =  'none';
    } 
}
document.getElementById('password').onkeypress = detectCapsLock;