What's the topmost iframe in the same domain?

How can I get the topmost iframe which is in the same domain, i.e.

iframe level 1 example.org
    iframe level 2 example.org
    iframe level 2 example.org 
        iframe level 3 example.org <-- sh开发者_开发百科ould return iframe level 1

iframe level 1 other-example.org
    iframe level 2 example.org
    iframe level 2 example.org 
        iframe level 3 example.org <-- should return iframe level 2

iframe level 1 other-example.org
    iframe level 2 example.org
    iframe level 2 example.org <-- should return iframe level 2 (this)

I need it because I have a website which should work in an iframe of another domain and stand-alone.

In this website there are scripts which depend on window.top which shouldn't be top but the topmost iframe in the same domain.

---

If you try to access the parent and it's from a different domain, you get an error. You could use this to recursively try to access the parent until it fails, something like:

function getTopIframe(win) {
  try {
    return getTopIframe(win.parent);
  } catch(e) {
    return win;
  }
}

Edit:

The topmost window is it's own parent, so you would need a check for that to prevent an eternal loop if the top window is in the same domain:

function getTopIframe(win) {
  try {
    if (win.parent != win) {
      return getTopIframe(win.parent);
    }
  } catch(e) {
  }
  return win;
}

---

Guffa's answer will not find the topmost same domain window in the perverse case where a window from a different domain sits between two same-domain windows. To handle that case we need to always traverse all the way to the topmost window and separately track windows from the same domain.

The implementation below does a couple of other nice things: (a) it uses the current window by default so it can be called without any arguments in the most common case and (b) it eliminates the unnecessary tail recursion in favor of a simple while loop.

function topSameDomainWindow(win) {
  win = win || window;
  var top = win;
  while (win.parent != win) {
    try {
      // Will throw when the parent window is from a different domain
      win.parent.document;
      top = win;
    } catch (e) {}
    win = win.parent;
  }
  return top;
}