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

这是一种解决方案，除了在写入时检查状态外，还在每次按下Caps Lock键时切换警告消息(有一些限制)。

它还支持A-Z范围之外的非英语字母，因为它根据toUpperCase()和toLowerCase()检查字符串字符，而不是根据字符范围检查。

$(function(){ //Initialize to hide caps-lock-warning $('.caps-lock-warning').hide(); //Sniff for Caps-Lock state $("#password").keypress(function(e) { var s = String.fromCharCode( e.which ); if((s.toUpperCase() === s && s.toLowerCase() !== s && !e.shiftKey)|| (s.toUpperCase() !== s && s.toLowerCase() === s && e.shiftKey)) { this.caps = true; // Enables to do something on Caps-Lock keypress $(this).next('.caps-lock-warning').show(); } else if((s.toLowerCase() === s && s.toUpperCase() !== s && !e.shiftKey)|| (s.toLowerCase() !== s && s.toUpperCase() === s && e.shiftKey)) { this.caps = false; // Enables to do something on Caps-Lock keypress $(this).next('.caps-lock-warning').hide(); }//else else do nothing if not a letter we can use to differentiate }); //Toggle warning message on Caps-Lock toggle (with some limitation) $(document).keydown(function(e){ if(e.which==20){ // Caps-Lock keypress var pass = document.getElementById("password"); if(typeof(pass.caps) === 'boolean'){ //State has been set to a known value by keypress pass.caps = !pass.caps; $(pass).next('.caps-lock-warning').toggle(pass.caps); } } }); //Disable on window lost focus (because we loose track of state) $(window).blur(function(e){ // If window is inactive, we have no control on the caps lock toggling // so better to re-set state var pass = document.getElementById("password"); if(typeof(pass.caps) === 'boolean'){ pass.caps = null; $(pass).next('.caps-lock-warning').hide(); } }); }); <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <input type="password" id="password" /> <span class="caps-lock-warning" title="Caps lock is on!">CAPS</span>

注意，只有在按下caps lock键之前知道caps lock的状态时，观察caps lock切换才有用。当前的大写锁定状态由密码元素上的caps JavaScript属性保持。这是当用户按下一个大写或小写字母时，我们第一次验证大写锁定状态时设置的。如果窗口失去焦点，我们就不能再观察到caps锁定切换，所以我们需要重置到未知状态。

反应

onKeyPress(event) { 
        let self = this;
        self.setState({
            capsLock: isCapsLockOn(self, event)
        });
    }

    onKeyUp(event) { 
        let self = this;
        let key = event.key;
        if( key === 'Shift') {
            self.shift = false;
        }
    }

    <div>
     <input name={this.props.name} onKeyDown={(e)=>this.onKeyPress(e)} onKeyUp={(e)=>this.onKeyUp(e)} onChange={this.props.onChange}/>
                {this.capsLockAlert()}
</div>

function isCapsLockOn(component, event) {
        let key = event.key;
        let keyCode = event.keyCode;

        component.lastKeyPressed = key;

        if( key === 'Shift') {
            component.shift = true;
        } 

        if (key === 'CapsLock') {
            let newCapsLockState = !component.state.capsLock;
            component.caps = newCapsLockState;
            return newCapsLockState;
        } else {
            if ((component.lastKeyPressed !== 'Shift' && (key === key.toUpperCase() && (keyCode >= 65 && keyCode <= 90)) && !component.shift) || component.caps ) {
                component.caps = true;
                return true;
            } else {
                component.caps = false;
                return false;
            }
        }
    }

如何使用getModifierState()

如果指定了修饰符，getModifierState()方法返回true 按键被按下或激活。

你可以这样使用它:

function checkIfCapsLockIsOn(event) {
  var capsLockIsOn = event.getModifierState("CapsLock");
  console.log("Caps Lock activated: " + capsLockIsOn);
}

这将简单地检查CapsLock是ON还是OFF，并在控制台显示它。你可以改变函数的工作方式。

然后在keydown或keyup上使用这个函数。

<input type="text" onkeydown="checkIfCapsLockIsOn(event)">

在jQuery中,

$('#example').keypress(function(e) { 
    var s = String.fromCharCode( e.which );
    if ( s.toUpperCase() === s && s.toLowerCase() !== s && !e.shiftKey ) {
        alert('caps is on');
    }
});

避免类似退格键的错误，需要s. tolowercase () !== s。

在下面的代码，它将显示警报时，Caps锁定，他们按下键使用shift。

如果返回false;那么当前字符将不会附加到文本页。

$('#password').keypress(function(e) { 
    // e.keyCode is not work in FF, SO, it will
    // automatically get the value of e.which.  
    var s = String.fromCharCode( e.keyCode || e.which );
    if ( s.toUpperCase() === s && s.toLowerCase() !== s && !e.shiftKey ) {
            alert('caps is on');
            return false;
    }
else  if ( s.toUpperCase() !== s) {
            alert('caps is on and Shiftkey pressed');
            return false;
    }
});