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!
![CSS Animations Between Media Queries]()
CSS animations are right up there with sliced bread. CSS animations are efficient because they can be hardware accelerated, they require no JavaScript overhead, and they are composed of very little CSS code. Quite often we add CSS transforms to elements via CSS during...
![CSS vs. JS Animation: Which is Faster?]()
How is it possible that JavaScript-based animation has secretly always been as fast — or faster — than CSS transitions? And, how is it possible that Adobe and Google consistently release media-rich mobile sites that rival the performance of native apps?
This article serves as a point-by-point...
![iPhone-Style Passwords Using MooTools PassShark]()
Every once in a while I come across a plugin that blows me out of the water and the most recent culprit is PassShark: a MooTools plugin that duplicates the iPhone's method of showing/hiding the last character in a password field. This gem of...
![HTML5 download Attribute]()
I tend to get caught up on the JavaScript side of the HTML5 revolution, and can you blame me? HTML5 gives us awesome "big" stuff like WebSockets, Web Workers, History, Storage and little helpers like the Element classList collection. There are, however, smaller features in...
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.