Resizing an iframe based on content

web-development

responsive-design

cross-domain

mutation-observer

byAlex Kataev·Dec 13, 2024

var iframe = document.getElementById('your-iframe-id'); // find an identity for our chameleon

iframe.onload = function() {   // onload event: our chameleon comes alive!
    iframe.style.height = iframe.contentWindow.document.body.scrollHeight + 'px'; // play the height-changing chameleon
};

Here, we simply bind the onload event to a function that resizes the iframe's height based on its content's scrollHeight. The iframe, in this case, acts as a chameleon that adjusts its size according to its environment (content), ensuring it neither chops off content nor leaves an abundance of white space.

Laying the groundwork of iframe resizing

iframe communication with postMessage

When dealing with cross-domain iframes, direct access to the iframe's DOM isn't possible due to the same-origin policy. However, JavaScript offers a method called postMessage() to enable cross-document messaging.

// Parent page sending a message to the iframe; message in a bottle
var iframeWin = document.getElementById('your-iframe').contentWindow;
iframeWin.postMessage('adjustHeight', 'https://iframed.domain.com');

// Inside the iframe — receiving end of the bottle message
window.addEventListener('message', function(event) {
    if (event.origin !== 'https://parent.domain.com') return; // did we get the message from a shady ship?
    if (event.data === 'adjustHeight') {
        parent.postMessage({  
            'frameHeight': document.body.scrollHeight   // return bottle with scrollHeight message
        }, event.origin);
    }
});

Handling dynamic changes

Frequent, significant changes to the iframe's content require us to detect DOM mutations. MutationObserver allows us to listen for changes in the iframe's content and adjust its dimensions as necessary, thereby answering the dynamic demands of the content.

Considering cache when resizing

To deal with browser caching issues, where resizing may get affected, you can append a cachebuster to your iframe URL. This ensures that each page load is unique and forces the browser to fetch new content rather than cached content.

Implementing seamless resizing

Apply a width of 100% to the iframe and define an initial height. The iframe, now responsive, adjusts its size based on the content.

Best practices to manage iframe size

Coordinating dynamic resizes

It's crucial to coordinate the resize function with the iframe's onload event. For communication with off-domain content, utilize a helper page. This ensures that even if the iframe content shifts, the container shape will follow suit.

Overflow handling

In cases where iframe's content might overflow, design the iframe with larger initial dimensions or use scrollbars.

Adapting per use-case

Remember that one shoe doesn't fit all; hence, the resizing strategy should be tailored to each use case. Pay close attention to whether it's a same-domain or cross-domain situation and whether the iframe content is static or dynamic.

A comprehensive resizing guide

Set up effective cross-domain resizing

Both iframed content and parent page must agree on message format and security checks. Implement listeners in both environments for safe and effective communication.

Tackle dynamic scenarios

Deploy a MutationObserver to automate the updates of iframe size according to the content's alterations. A handy tool for responsive iframes with dynamic content!

Prioritize performance and security

Seek simpler and consistent methods compliant with web security standards. Keep away from parsing complex JavaScript codes, especially from external domains.