Lazy Load IFRAMEs

By  on  

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:

See the Pen IFRAME Lazy Load by David Walsh (@darkwing) on CodePen.

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!

Recent Features

Incredible Demos

  • By
    prefers-color-scheme: CSS Media Query

    One device and app feature I've come to appreciate is the ability to change between light and dark modes. If you've ever done late night coding or reading, you know how amazing a dark theme can be for preventing eye strain and the headaches that result.

  • By
    MooTools Typewriter Effect Plugin

    Last week, I read an article in which the author created a typewriter effect using the jQuery JavaScript framework. I was impressed with the idea and execution of the code so I decided to port the effect to MooTools. After about an hour of coding...

Discussion

  1. 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.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!