If you google for “how to detect clicks outside of an element,” you’ll find that the top result on stackoverflow suggests binding a click handler on the html element that should perform the desired action, and another click handler on the element itself that calls event.stopPropagation().

$('html').click(function() {
  // code to execute when clicked outside of #container
$('#container').click(function(event) {

This works because of event bubbling, where clicking on an element will call its click handlers, and then its parent’s click handlers, and then its grandparent’s click handlers, and so on until the root (html) element’s click handlers are called, or until event.stopPropagation() is called in a click handler on the way up, whichever occurs first. So, the idea is that clicking anywhere outside of the element will eventually call the click handler on html, and clicking anywhere inside of the element will eventually run into an event.stopProparagation().

The problem with this approach is that if other elements outside of #container also have click handlers that call stopPropagation(), the html click handler will never be called, and this is just a straight up bug.

A more robust way to detect clicks outside of an element is to register a click handler on document for the event capturing phase, and tell the handler to perform an action only if the target (clicked) element is not a child of the element for which you want to detect clicks outside.

The event capturing phase comes before the event bubbling phase and traverses the DOM in reverse order. We start at the root element and go down the DOM hierarchy until the target element is reached, triggering the click handlers (that were specified to be triggered during the event capturing phase) on each element on the way. This blog post by Sam Stephenson has some of the best depictions of event bubbling and event capturing.

Adding an event handler that gets called in the event capturing case requires plain ol' javascript. JQuery does not provide a way to do this, probably because IE8 and below do not support event capturing. The code looks something like this:

document.addEventListener('click', function(e) {
  if (!document.getElementById('container').contains(e.target)) {
    // code to execute when clicked outside of #container
}, true);

The third argument to addEventListener specifies whether the event handler should be called during the event capturing phase. The guard conditional checks whether #container is an ancestor of the clicked element, and do nothing if it is. If it isn’t, then it means something was clicked outside of #container and the code will execute.