Dynamically set fancybox 3 iframe size - fancybox

Question

When dealing with dynamically sizing the iframe in fancybox, I accidentally found that setting data-width and data-height on the [data-fancybox] is helpful after reading this answer.
Exmaple HTML element:
<a data-fancybox data-width="<?= $banner_width; ?>" data-height="<?= $banner_height; ?>" data-src="example.com" href="javascript:;">example.com</a>
and js:
$("[data-fancybox]").fancybox({
afterLoad: function ( instance, slide ) {
$('body').find('.fancybox-content').css({"width": slide.opts.width + "px", "height": slide.opts.height + "px"});
}
});
What I couldn't figure out is that there is no explanation of data-width and data-height usage on HTML element from fancybox documentation (please correct me if I'm wrong).
NOTE: these two code snippets above do work for me, but they have to work together, it wouldn't work if one of them is taken off.
Can anyone explain that a little bit for me please?

Answer 1

Based on fancybox 3 documentation, they do offer a way to set our own custom options by creating data-options attribute. Here is the example from the documentation:
<a data-fancybox
data-options='{"caption" : "My caption", "src : "iframe.html"}' href="javascript:;">
Open external page using iframe
</a>
You can see the value of these options by console.info( slide.opts ) from the callback function like onComplete (slide is one argument in the callback function ).
Not surprisingly, these two snippets are the same:
<a data-fancybox data-width="<?= $banner_width; ?>" data-height="<?= $banner_height; ?>" data-src="example.com" href="javascript:;">example.com</a>
<a data-fancybox data-options='{"width" : "<?= $banner_width; ?>", "height" : data-height="<?= $banner_height; ?>", "src" : "example.com" }' href="javascript:;">example.com</a>
So, in my javascript, I use slide.opts.width to get the value from data-width and slide.opts.heightto get the height from data-height, that is how my width and height value get passed from backend to frontend.
Since these two values are processed in afterLoad callback, so every iframe will be initiated with different width and height.

Answer 2

Properties - data-width and data-height - are used to tell the script real dimension of the image. The script then can calculate position and start zooming thumbnail while real image is still loading.
See documentation - http://fancyapps.com/fancybox/3/docs/#images
These properties are not used anywhere else.
You can use { iframe : { css : { width: '', height : '' } } } to set iframe element width/height, but there is no option to change iframe content.