<animated-highlight>

The element <animated-highlight> does precisely one thing: it slots another element and switches classes on it. Its use case is to serve as a sort of runtime for code generated by diff2gif.com. The element is extremely basic and meant to be hacked and extended by you, the user.

HTML API

General usage

The element <animated-highlight> is a custom element with several slots, attributes, and DOM properties for customization. To get it working, just include dist/bundle.js in a script tag in your web page! A minimal example:

<script src="dist/bundle.js"></script>
<animated-highlight controls keyframes="0 1 2 3">
  <div>Switch classes on me!</div>
</animated-highlight>

This will cycle classes on the div element wrapped by the custom elements from frame0 to frame1 to frame2 to frame3. The keyframes are defined as a whitespace-separated list of numbers in the keyframes attribute while the existence of the controls attribute provides basic forwards/backwards buttons.

Attribute summary:

• controls: When present, shows controls UI (by default just a pair of forwards/backwards buttons). Reflected by the DOM property controls
• keyframes: Defines the list of keyframes with a value of whitespace-separated positive integers. Values that are anything but a list of whitespace-separated numbers are equal to the attribute missing (eg. there are no keyframes at all in this case). The list of keyframes is always sorted in ascending order and cleared of any duplicates or non-numbers. Negative numbers are interpreted as positive numbers.
• current: Indicates the current frame. Can be changed to change the current frame. Reflected by the DOM property current. Values that are anything but a positive integer are treated as 0.

Custom controls

The default control UI for the element is basic and ugly. There are three options to remedy this:

1. Wrap the element

You can simply wrap an <animated-highlight> element without a controls attribute and add your own custom logic that uses the JavaScript API described below. This is probably the way to go for integration in Frameworks like React.

2. Style the controls

If you just want to reposition and re-style the existing controls, you can use the following CSS ::part() selectors:

• animated-highlight::part(controls): The container element for the buttons
• animated-highlight::part(controls-prevBtn): The "previous" buttons
• animated-highlight::part(controls-nextBtn): The "next" buttons

The buttons are <button> elements with <span> element inside.

3. Replace the controls

The default controls are actually just fallback content for a shadow DOM slot. This means that you can very easily just add your own:

<animated-highlight controls keyframes="0 1 2 3">
  <div>Switch classes on me!</div>
  <div slot="controls">
    <div data-command="prev">Back</div>
    <div data-command="next">Next</div>
  </div>
</animated-hightlight>

All you need to do to make your custom buttons (in this case, <div> elements) work is add the attributes <div data-command="prev">Back</div> and <div data-command="next">Next</div> respectively. You can also build up your custom controls to do way more than just provide two buttons. See demo/index.html for an example.

4. Hack the element

The element's shadow root is open and most of the private properties on the AnimatedHighlight class are actually private. Go and mess with 'em!

JavaScript API

This package provides an ECMAScript module that exports the class for the custom element. To get it working, import the class from the module and register it as a new element:

import { AnimatedHighlight } from "animated-highlight";

window.customElements.get("animated-highlight") ??
  window.customElements.define("animated-highlight", AnimatedHighlight);

getter/setter controls (boolean)

Reflects the HTML attribute controls. Setting this property to a falsy value removes the attribute.

getter/setter current (number)

Reflects the current keyframe. The setter coerces and rounds values to whole numbers and clamps them to the range of available keyframes.

getter nextCurrent (number | null)

Reflects the keyframe the element is about to switch to during an ah-beforeframechange event. This property is only set to a number during this event and returns null at any other time.

getter maxFrame (number)

Returns the last keyframe.

getter/setter keyframes (Array)

Reflects the HTML attribute keyframes. Setting this property to anything but an array is equal to setting the property to an empty array.

methods next() and prev()

Go to the next or previous keyframe respectively, unless the corresponding beforeframechange event gets cancelled. Returns a number indicating the new keyframe.

Event ah-beforeframechange (bubbles, cancelable, not composed)

Fires before a frame change occurs. Call preventDefault() on the event to stop the frame change from happening. You can inspect the event target's current property to figure out the current frame and the event target's nextCurrent property to see what the next frame is going to be... and then decide whether or not you want to to stop the frame change.

Event ah-afterframechange (bubbles, not cancelable, not composed)

As the name suggests, this is fired after a frame change has occurred.

Notes

Neither dom properties nor HTML attributes for the events ah-beforeframechange and ah-afterframechange are implemented! You must use addEventListener(), attributes or properties like onAhAfterframechange = ... are not supported.

Integrations

TypeScript

The module provides types for the element's class AnimatedHighlight and adds its declarations into HTMLElementTagNameMap. This ensures that built-ins like document.createElement() know how to handle the new tag name animated-highlight. Unless you want to use another tag name or integrate with special HTML snowflakes like react, you don't have to do anything.