Detect iFrame embedding in Javascript

Question

I have an application that has a certain page -- let's call it Page A. Page A is sometimes a top-level page, but also sometimes is embedded as an iframe within page B. All pages come from the same server and there are no cross-domain issues.

I have a greasemonkey script that runs on page A. How can the greasemonkey script detect whether page A is within the iframe context or not?

Answer 1

Looking at frame length breaks down generally if page A itself has frames (I know this might not be the case for this specific instance). The more reliable and meaningful test would be:

if (window!=window.top) { /* I'm in a frame! */ }