Detect Caps Lock with JavaScript

By  on  

Anyone is capable of having their caps lock key on at any given time without realizing so. Users can easily spot unwanted caps lock when typing in most inputs, but when using a password input, the problem isn't so obvious. That leads to the user's password being incorrect, which is an annoyance. Ideally developers could let the user know their caps lock key is activated.

To detect if a user has their keyboard's caps lock turn on, we'll employ KeyboardEvent's getModifierState method:

document.querySelector('input[type=password]').addEventListener('keyup', function (keyboardEvent) {
    const capsLockOn = keyboardEvent.getModifierState('CapsLock');
    if (capsLockOn) {
        // Warn the user that their caps lock is on?
    }
});

I'd never seen getModifierState used before, so I explored the W3C documentation to discover other useful values:

dictionary EventModifierInit : UIEventInit {
  boolean ctrlKey = false;
  boolean shiftKey = false;
  boolean altKey = false;
  boolean metaKey = false;

  boolean modifierAltGraph = false;
  boolean modifierCapsLock = false;
  boolean modifierFn = false;
  boolean modifierFnLock = false;
  boolean modifierHyper = false;
  boolean modifierNumLock = false;
  boolean modifierScrollLock = false;
  boolean modifierSuper = false;
  boolean modifierSymbol = false;
  boolean modifierSymbolLock = false;
};

getModifierState provides a wealth of insight as to the user's keyboard during key-centric events. I wish I had known about getModifier earlier in my career!

Recent Features

Incredible Demos

  • By
    Animated Progress Bars Using MooTools: dwProgressBar

    I love progress bars. It's important that I know roughly what percentage of a task is complete. I've created a highly customizable MooTools progress bar class that animates to the desired percentage. The Moo-Generated XHTML This DIV structure is extremely simple and can be controlled...

  • By
    iPhone Click Effect Using MooTools or jQuery

    One thing I love about love about Safari on the iPhone is that Safari provides a darkened background effect when you click a link. It's the most subtle of details but just enforces than an action is taking place. So why not implement that...

Discussion

  1. Great to know, thanks! Even has modifierHyper!

  2. Craig

    How about they just get rid of CAPS LOCK keys, or relegate them to a far off corner of the keyboard?

    It is the most useless key, taking up real estate in a valuable position.

    At a minimum, the OS should allow for a key re-assignment.

    I HATE CAPS LOCK keys. And did not use it once in this rant.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!