Lazy Load IFRAMEs
We've known for a decade that lazy loading resources like JavaScript, CSS, and especially images is a massive performance win for web pages. At first we used tricks and JavaScript to do the lazy loading, but more recently native image lazy loading has debuted in browsers.
Did you know that you can also lazy load IFRAMEs using the same loading="lazy" attribute and value?
<iframe
src="https://davidwalsh.name/"
loading="lazy"
onload="alert('Loaded!');"
/>
You can see how lazy loading IFRAMEs works with this demo:
This single attribute to perform a complex but useful operation is the ideal solution for lazy loading just about anything. I'm so thankful that browsers are implementing APIs that make using best practices so easy!
![JavaScript Promise API]()
While synchronous code is easier to follow and debug, async is generally better for performance and flexibility. Why "hold up the show" when you can trigger numerous requests at once and then handle them when each is ready? Promises are becoming a big part of the JavaScript world...
![Being a Dev Dad]()
I get asked loads of questions every day but I'm always surprised that they're rarely questions about code or even tech -- many of the questions I get are more about non-dev stuff like what my office is like, what software I use, and oftentimes...
![JavaScript Copy to Clipboard]()
"Copy to clipboard" functionality is something we all use dozens of times daily but the client side API around it has always been lacking; some older APIs and browser implementations required a scary "are you sure?"-style dialog before the content would be copied to clipboard -- not great for...
![Image Manipulation with PHP and the GD Library]()
Yeah, I'm a Photoshop wizard. I rock the selection tool. I crop like a farmer. I dominate the bucket tool. Hell, I even went as far as wielding the wizard wand selection tool once.
...OK I'm rubbish when it comes to Photoshop.
This browser feature looks really like a huge gamechanger. Would love so much to use it with profit although it doesn’t seem to work correctly for me.
[First of all, using it with images instead of iframes always worked perfectly, so all this regards only loading=”lazy” for iframes.]
After hours of testing on different pages, what I see is that using loading=”lazy”, Iframes load WAY TOO EARLY.
This apparently buggy behavior happens only if the page itself is NOT loaded from another iframe. So this rules out CodePen as a viable tool to show this.
Let’s make a text.html file from this code, almost identical to your example, to highlight exactly what I’m saying:
https://gist.github.com/jeff-at-livecanvas/bb1a803465419c62d623305daf6722cd
Opening this file in a Chrome window, with an internal height of 700 pixels, shows the Loaded! message immediately.
Same happens with latest Firefox too.
Would be great if somebody could shed some light on this.