Get Cross-Domain iFrame content

I would like to know how I can get content from an 开发者_运维问答IFrame cross-domain?

I have no problem getting content from a non-cross-domain iFrame, but when it's located on another domain, JavaScript doesn't allow access.

You use Cross Document Messaging, here's an example. Here's the significant code from the parent page:

window.addEventListener('message', receiver, false);
function receiver(e) {
    document.getElementById('message').value = e.data;
}
function update_child() {
    var el = document.getElementsByTagName('iframe')[0];
    el.contentWindow.postMessage('Updated from parent', '*');
}

The child page has identical code - note that you need to be able to implement the interface on both domains for this to work, either by yourself, if you control both, or in co-operation with the owner of the other domain. In production code you should set (and check) the origin.

Short of requesting it via a proxy on your own server, you can't.

The same origin policy prevents it (and for good reason; I would be very unhappy if you loaded my banking site in your iframe and read all my account details)