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

  • By
    5 HTML5 APIs You Didn’t Know Existed

    When you say or read "HTML5", you half expect exotic dancers and unicorns to walk into the room to the tune of "I'm Sexy and I Know It."  Can you blame us though?  We watched the fundamental APIs stagnate for so long that a basic feature...

  • By
    Responsive and Infinitely Scalable JS Animations

    Back in late 2012 it was not easy to find open source projects using requestAnimationFrame() - this is the hook that allows Javascript code to synchronize with a web browser's native paint loop. Animations using this method can run at 60 fps and deliver fantastic...

Incredible Demos

  • By
    AJAX For Evil:  Spyjax with jQuery

    Last year I wrote a popular post titled AJAX For Evil: Spyjax when I described a technique called "Spyjax": Spyjax, as I know it, is taking information from the user's computer for your own use — specifically their browsing habits. By using CSS and JavaScript, I...

  • By
    MooTools CountDown Plugin

    There are numerous websites around the internet, RapidShare for example, that make you wait an allotted amount of time before presenting you with your reward. Using MooTools, I've created a CountDown plugin that allows you to easily implement a similar system. The MooTools JavaScript The CountDown class...

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!