Animations

Htmx is designed to allow you to use CSS transitions to add smooth animations and transitions to your web page using only CSS and HTML. Below are a few examples of various animation techniques.

Basic CSS Animations

Color Throb

The simplest animation technique in htmx is to keep the id of an element stable across a content swap. If the id of an element is kept stable, htmx will swap it in such a way that CSS transitions can be written between the old version of the element and the new one.

Consider this div:

<style>
.smooth {
  transition: all 1s ease-in;
}
</style>
<div id="color-demo" class="smooth" style="color:red"
      hx-get="/colors" hx-swap="outerHTML" hx-trigger="every 1s">
  Color Swap Demo
</div>

This div will poll every second and will get replaced with new content which changes the color style to a new value (e.g. blue):

<div id="color-demo" class="smooth" style="color:blue"
      hx-get="/colors" hx-swap="outerHTML" hx-trigger="every 1s">
  Color Swap Demo
</div>

Because the div has a stable id, color-demo, htmx will structure the swap such that a CSS transition, defined on the .smooth class, applies to the style update from red to blue, and smoothly transitions between them.

Demo

Smooth Progress Bar

The Progress Bar demo uses this basic CSS animation technique as well, by updating the length property of a progress bar element, allowing for a smooth animation.

Swap Transitions

Fade Out On Swap

If you want to fade out an element that is going to be removed when the request ends, you want to take advantage of the htmx-swapping class with some CSS and extend the swap phase to be long enough for your animation to complete. This can be done like so:

<style>
.fade-me-out.htmx-swapping {
  opacity: 0;
  transition: opacity 1s ease-out;
}
</style>
<button class="fade-me-out"
        hx-delete="/fade_out_demo"
        hx-swap="outerHTML swap:1s">
        Fade Me Out
</button>

Demo

Delete Me

Settling Transitions

Fade In On Addition

Building on the last example, we can fade in the new content by using the htmx-added class during the settle phase. You can also write CSS transitions against the target, rather than the new content, by using the htmx-settling class.

<style>
#fade-me-in.htmx-added {
  opacity: 0;
}
#fade-me-in {
  opacity: 1;
  transition: opacity 1s ease-out;
}
</style>
<button id="fade-me-in"
        hx-post="/fade_in_demo"
        hx-swap="outerHTML settle:1s">
        Fade Me In
</button>

Demo

Fade Me In

Request In Flight Animation

You can also take advantage of the htmx-request class, which is applied to the element that triggers a request. Below is a form that on submit will change its look to indicate that a request is being processed:

<style>
  form.htmx-request {
    opacity: .5;
    transition: opacity 300ms linear;
  }
</style>
<form hx-post="/name">
<label>Name:</label><input name="name"><br/>
<button>Submit</button>
</form>

Demo

Using the HTMX class-tools Extension

Many interesting animations can be created by using the class-tools extension.

Here is an example that toggles the opacity of a div. Note that we set the toggle time to be a bit longer than the transition time. This avoids flickering that can happen if the transition is interrupted by a class change.

<style>
.demo.faded {
  opacity:.3;
}
.demo {
  opacity:1;
  transition: opacity ease-in 900ms;
}
</style>
<div class="demo" classes="toggle faded:1s">Toggle Demo</div>

Demo

Conclusion

You can use the techniques above to create quite a few interesting and pleasing effects with plain old HTML while using htmx.