How do I find out which DOM element has the focus?

Use document.activeElement, it is supported in all major browsers.

Previously, if you were trying to find out what form field has focus, you could not. To emulate detection within older browsers, add a "focus" event handler to all fields and record the last-focused field in a variable. Add a "blur" handler to clear the variable upon a blur event for the last-focused field.

If you need to remove the activeElement you can use blur; document.activeElement.blur(). It will change the activeElement to body.

Related links:

• activeElement Browser Compatibility
• jQuery alternative for document.activeElement

As said by JW, you can't find the current focused element, at least in a browser-independent way. But if your app is IE only (some are...), you can find it the following way:

document.activeElement

It looks like IE did not have everything wrong after all, this is part of HTML5 draft and seems to be supported by the latest version of Chrome, Safari and Firefox at least.

document.activeElement is now part of the HTML5 working draft specification, but it might not yet be supported in some non-major/mobile/older browsers. You can fall back to querySelector (if that is supported). It's also worth mentioning that document.activeElement will return document.body if no element is focused — even if the browser window doesn't have focus.

The following code will work around this issue and fall back to querySelector giving a little better support.

var focused = document.activeElement;
if (!focused || focused == document.body)
    focused = null;
else if (document.querySelector)
    focused = document.querySelector(":focus");

An addition thing to note is the performance difference between these two methods. Querying the document with selectors will always be much slower than accessing the activeElement property. See this jsperf.com test.

If you can use jQuery, it now supports :focus, just make sure you are using version 1.6+.

This statement will get you the currently focused element.

$(":focus")

From: How to select an element that has focus on it with jQuery