The FocusEvent.relatedTarget property refers to the the secondary target of a focus event. Depending on the type of focus event, this is either the element losing focus (for focus and focusin) or the element receiving focus (for blur and focusout).

This is handy when you need to know which was the last element in focus, or which will be the next element in focus.

The focus and focusin events

The focus event fires when an element receives focus; the focusin event fires when an element is about to receive focus. The main difference is that the former doesn't support event bubbling, while the latter does.

For the focus and focusin events:

  • The target property refers to the element receiving focus.
  • The relatedTarget property refers to the element losing focus (if any).

The blur and focusout events

The blur event fires when an element loses focus; the focusout event fires when an element is about to lose focus. The main difference is that the former doesn't support event bubbling, while the latter does.

For the blur and focusout events:

  • The target property refers to the element losing focus.
  • The relatedTarget property refers to the element receiving focus (if any).

A note on null

Not all elements are focusable, meaning the relatedTarget property may be null. The MDN Web Docs say that relatedTarget may also be set to null for security reasons, like when tabbing in or out of a page.

An example

Here's a simple example. It listens to all focusin and focusout events in the document body, logging the values of the target and relatedTarget properties for comparison:

/**
* Handle focusin and focusout events.
* @param {FocusEvent} event - The FocusEvent interface.
*/

function handleFocus(event) {
// Log the event type
console.log(event.type.toUpperCase());

// Log the target and relatedTarget
console.log('target:', event.target);
console.log('relatedTarget:', event.relatedTarget);

// Log a newline character
console.log('\n');
}

// Handle focusin and focusout events
document.body.addEventListener('focusin', handleFocus);
document.body.addEventListener('focusout', handleFocus);

You can view the demo on CodePen.