With different domains, it is not possible to call methods or access the iframe's content document directly.
You have to use cross-document messaging.
For example in the top window:
myIframe.contentWindow.postMessage('hello', '*');
and in the iframe:
window.onmessage = function(e){
if (e.data == 'hello') {
alert('It works!');
}
};
If you are posting message from iframe to parent window
window.top.postMessage('hello', '*')