Call parent Javascript function from inside an iframe

I know this is an old question, but in case the accepted answer doesn't work (it didn't work for me) you could do this inside parent.js

window.myfunction = function () {
   alert("I was called from a child iframe");
}

Now from the iframe you can call myfunction() like you initially wanted

window.parent.myfunction(); 

Window.postMessage() method safely enables cross-origin communication.

If you have access to parent page then any data can be passed as well as any parent method can be called directly from Iframe.

Parent page:

if (window.addEventListener) {
    window.addEventListener("message", onMessage, false);        
} else if (window.attachEvent) {
    window.attachEvent("onmessage", onMessage, false);
}

function onMessage(event) {
    // Check sender origin to be trusted
    if (event.origin !== "http://example.com") return;

    var data = event.data;      
    if (typeof(window[data.func]) == "function") {
        window[data.func].call(null, data.message);
    }
}

// Function to be called from iframe
function parentFuncName(message) {
    alert(message);
}

Iframe code:

window.parent.postMessage({
    'func': 'parentFuncName',
    'message': 'Message text from iframe.'
}, "*");

References:

• Cross-document messaging (https://html.spec.whatwg.org/multipage/comms.html#web-messaging)
• Window.postMessage method (https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage)
• Can I Use (http://caniuse.com/#search=postMessage)