A JavaScript function that will tell you if an element is within another element. This is useful for things like closing a widget when a user clicks somewhere else in the page.

within.js

function within(needle, haystack) {

  // If the parent element is the target
  if (needle === haystack) {
    return true;

  // If any of the children are the target
  } else if (haystack.firstChild) {
    var child = haystack.firstChild;
    do {
      if (within(needle, child)) return true;
    } while(child = child.nextSibling);
  }

}

if (within(a, b)) alert(a + " is within " + b);