Detect Caps Lock with JavaScript "w3c.github.io/uievents/#event-modifier-initializers"

detect_capslock.js

document.querySelector('input[type=password]').addEventListener('keyup', function (keyboardEvent) {
    const capsLockOn = keyboardEvent.getModifierState('CapsLock');
    if (capsLockOn) {
        console.log('Caps Lock is ON');
    } else {
        console.log('Caps Lock is OFF');
    }
});