Debugging iframes with Chrome developer tools
DebuggingIframeGoogle ChromeDebugging Problem Overview
I'd like to use the Chrome developer console to look at variables and DOM elements in my app, but the app exists inside an iframe (since it's an OpenSocial app).
So the situation is:
<containing site>
<iframe id='foo' src='different domain'>
... my app ...
</iframe>
</containing site>
Is there any way to access things happening in that iframe from the developer console? If I try to do document.getElementById("foo").something, it doesn't work, probably because the iframe is in a different domain.
I can't open the iframe contents in a new tab, because the iframe needs to be able to talk to the containing site as well.
Debugging Solutions
Solution 1 - Debugging
In the Developer Tools in Chrome, there is a bar along the top, called the Execution Context Selector (h/t felipe-sabino), just under the Elements, Network, Sources... tabs, that changes depending on the context of the current tab. When in the Console tab there is a dropdown in that bar that allows you to select the frame context in which the Console will operate. Select your frame in this drop down and you will find yourself in the appropriate frame context. :D
Chrome v59
Chrome v33
Chrome v32 & lower
Solution 2 - Debugging
Currently evaluation in the console is performed in the context of the main frame in the page and it adheres to the same cross-origin policy as the main frame itself. This means that you cannot access elements in the iframe unless the main frame can. You can still set breakpoints in and debug your code using Scripts panel though.
Update: This is no longer true. See Metagrapher's answer.
Solution 3 - Debugging
When the iFrame points to your site like this:
<html>
<head>
<script type="text/javascript" src="/jquery.js"></script>
</head>
<body>
<iframe id="my_frame" src="/wherev"></iframe>
</body>
</html>
You can access iFrame DOM through this kind of thing.
var iframeBody = $(window.my_frame.document.getElementsByTagName("body")[0]);
iframeBody.append($("<h1/>").html("Hello world!"));
Solution 4 - Debugging
In my fairly complex scenario the accepted answer for how to do this in Chrome doesn't work for me. You may want to try the Firefox debugger instead (part of the Firefox developer tools), which shows all of the 'Sources', including those that are part of an iFrame