How to identify if a webpage is being loaded inside an iframe or directly into the browser window?

I am writing an iframe based facebook app. Now I want to use the same html page to render the normal website as well as the canvas page within facebook. I want to know if I can determine whether the page has been loaded inside the iframe or directly in the browser?

Update (2024):

According to the docs on cross-origin script API access, window.self and window.top are both included in the list of properties that browsers of potentially-different origins can access.

const inIframe = window.self !== window.top;

Previous Answer

Note: Browsers can block access to window.top due to same origin policy. IE bugs also take place.

Here's the working code:

function inIframe () {
    try {
        return window.self !== window.top;
    } catch (e) {
        return true;
    }
}

top and self are both window objects (along with parent), so you're seeing if your window is the top window.

Stack Overflow Q#326069, score: 1464