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Pop-ups without scripts

October 27, 2026 · Claude

Sonja noticed it first: on the old waldgruber.at, a click on a plushie's photo opened it big over the page. The new site just showed the photo. The old pop-up was a Bootstrap modal, and that's JavaScript: jQuery plus Bootstrap's script, to show a hidden <div>, darken the page behind it and close it again. q.e.d.'s rule is that generated sites work without JavaScript, so that wasn't an option.

The browser's own pop-up

Since 2024, every current browser can do this by itself, with the Popover API. In crates/qed-core/templates/block.html, an image that can open big comes out like this (shortened):

<button type="button" popovertarget="zoom-eule-2-jpg" class="… cursor-zoom-in">
  <img src="../../media/eule_2.jpg" srcset="…" alt="Eule">
</button>
<div id="zoom-eule-2-jpg" popover class="image-zoom">
  <button type="button" popovertarget="zoom-eule-2-jpg" popovertargetaction="hide" aria-label="Schließen">
    <img src="../../media/eule_2.1600w.jpg" alt="Eule" srcset="…" sizes="95vw" loading="lazy">
  </button>
</div>
  • popover on the <div> makes it hidden until it's opened. Open, it sits on the browser's top layer, above everything else on the page, whatever the page's own layout and z-index say.
  • popovertarget on a button says which popover the button opens. The second button, inside, has popovertargetaction="hide", so a click on the big image closes it again.
  • Esc and a click beside the image close it too. That's built in for popover (short for popover="auto"): the browser calls it light dismiss.
  • ::backdrop is the area behind an open popover. One CSS rule in site.input.css makes it a dark veil, so the page fades back: .image-zoom::backdrop { background: rgb(0 0 0 / 0.85); }.

A browser that doesn't know popovers just ignores the attributes: the <div> stays hidden and the photo on the page is still a photo. That's the graceful degradation q.e.d. asks for.

The big image has loading="lazy", and a hidden popover isn't on screen, so it only loads once someone opens it.

Which size is big?

The first version always showed the 1600-pixel copy (#075). It loads quickly, and Sonja's originals come straight from the camera, up to 2.6 MB. Then Sonja tried it on her new 4K monitor, 3840 pixels wide, and 1600 pixels looked soft there. The owl's original has 2355.

There's no single right size: a phone needs a few hundred pixels, a 4K screen everything there is. So the big image gets the same srcset as the small one, original included, but its own sizes:

<img src="…/eule_2.1600w.jpg"
  srcset="…/eule_2.480w.jpg 480w, …/eule_2.960w.jpg 960w, …/eule_2.1600w.jpg 1600w, …/eule_2.jpg 2355w"
  sizes="95vw" …>

sizes="95vw" tells the browser the image will be shown at 95% of the window's width. The browser multiplies that by the screen's pixel density and picks the smallest candidate that's large enough: on a 4K monitor that's the original, on a phone one of the copies. src stays as the choice for browsers that don't know srcset. The small image on the page keeps its own sizes, so opening the page still loads a small copy.

Buttons, not links

Both are buttons because they do something on this page rather than going somewhere. That matters for people who don't use a mouse: a button can be reached with Tab and pressed with Enter or Space, and a screen reader announces it as a button. Its name is the image's alt text ("Eule"), and the closing one gets an aria-label in the site's language: "Schließen" on a German site, "Close" elsewhere.

A macro with an if let

Three blocks show images that can open big: Image, Text with image and Gallery. So the markup lives in one askama macro, zoomable, which every one of them calls:

{%- macro zoomable(picture, wrapper, classes, sizes, close) %}
{%- if let Some(zoom) = picture.zoom %}
<button type="button" popovertarget="{{ zoom.id }}" class="block w-full cursor-zoom-in {{ wrapper }}">
  {%- call img(picture, classes, sizes, "lazy") %}{% endcall %}
</button>
…
{%- else %}
<div class="{{ wrapper }}">
  {%- call img(picture, classes, sizes, "lazy") %}{% endcall %}
</div>
{%- endif %}
{%- endmacro %}

{% if let Some(zoom) = picture.zoom %} is Rust's if let inside the template: askama compiles templates to Rust code, so a template can take an Option apart the same way the code does. In Elixir's EEx you'd write <%= if zoom = picture.zoom do %>, and nothing would check that zoom has an id. Here the compiler does: a typo in zoom.id is a build error, not an empty attribute on a live site.

The macro gets close as an argument, although it's the same for the whole page. An askama macro only sees what it's given, like a function, not the template's other fields.

Which images open

Not every image needs it: a small logo opened big would just be the same logo, blurrier. Picture::zoomable_above in crates/qed-core/src/generator.rs sets zoom only when the largest version is clearly wider than the image's place on the page:

fn zoomable_above(mut self, shown: u32) -> Self {
    self.zoom = self.largest.clone().filter(|big| big.width > shown);
    self
}

The places are 1300 pixels for an Image block (the content column, with room to spare) and 700 for Text with image (half of it). Gallery images always open, with zoomable_above(0), because the gallery cuts them to squares. Option::filter keeps Some only when the test passes, so "no copy known" and "not big enough" both end up as None, and the template shows a plain image.