Invoking JavaScript code in an iframe from the parent page

Cross-browser frame referencing

Different browsers have varying interpretations of standards. To cater to all, use contentWindow and contentDocument.defaultView for universally applicable iframe references:

// Line 1: Identify the iframe by ID
// Line 2: Cater to several browser's methods of referencing iframe's window
var iframe = document.getElementById('myIframe');
var iframeWindow = iframe.contentWindow || iframe.contentDocument.defaultView;

// DON'T PANIC! Calling the function 🚀 
iframeWindow.myFunction();


Care to invoke functions only when the iframe is fully loaded. For this, add a load event listener to the iframe:

// Can't call a function if the iframe is still caught in traffic! 🚥
document.getElementById('myIframe').addEventListener('load', function() {
    this.contentWindow.myFunction();
});


Security and cross-origin practices

Cross-origin iframes bring along security implications. Resort to window.postMessage() for safe cross-origin message exchanges. Don't forget to verify the sender's origin within the event handler:

// Parent page: Sending a secret message (Shhh! 🤫)
var iframe = document.getElementById('myIframe');
iframe.contentWindow.postMessage('yourMessage', 'https://expected-origin.com');

// iframe: Validating incoming messages. No spam, please! 🚫
window.addEventListener('message', (event) => {
    if (event.origin !== 'https://trusted-origin.com') return;
    // Safely handle the message
}, false);


Error alerts

Ensure to gracefully handle errors when invoking iframe functions. Use try-catch blocks to alert about potential hiccups:

try {
    // Just calling a function, what can go wrong? 🤷‍♀️
    document.getElementById('myIframe').contentWindow.myFunction();
} catch (e) {
    // Apparently, a lot can go wrong! 🥵
    console.error('Error invoking function in iframe: ', e);
}


Communication readiness

In dynamic scenarios, the iframe informs the parent when it's ready for interaction. Implement a callback mechanism or an event-based system for better interaction:

// iframe: "All systems are go! 🚀"
window.parent.postMessage('iframeReady', '*');

// Parent page: "Great! Execute function now."
window.addEventListener('message', (event) => {
    if (event.data === 'iframeReady') {
        document.getElementById('myIframe').contentWindow.myFunction();
    }
}, false);


Messaging API insights

Digging deep into the web messaging API? W3C documentation is a fantastic resource. It offers insight into securely transmitting messages between distinct origins.

Named iframe invocation

Why not target iframes by name using window.frames:

// Invoking the function in named iframe like a boss 😎
window.frames['iframeName'].myFunction();


This method is extremely handy when dealing with multiple iframes and unique identifiers make more sense than vague indices.