README.md

@lit-labs/motion

Lit directives for making things move.

Installation

From inside your project folder, run:

$ npm install @lit-labs/motion

Animate directive

The animate directive can be used to animate DOM elements from one lit render to the next. If the animate element changes state between renders, the directive performs a "tweening" animation between the two states based on the options given. In addition, elements can animate when they initially render to DOM and when they are removed.

The directive supports a number of options:

Option	Usage
keyframeOptions	configure animation via standard KeyframeAnimationOptions
properties	list of properties to animate, defaults to ['left', 'top','width', 'height', 'opacity', 'color', 'background']
disabled	disables animation
guard	function producing values that must change for the animate to run
in	keyframes to use when animating in
out	keyframes to use when animating out
skipInitial	skip animating in the first time
id	used to link to other animate's via inId
inId	id of the animate to render from when animating in
onStart	run when the animate starts
onComplete	run when the animate completes
onFrames	run when the frames are produced, use to modify frames

How it works

The directive uses the FLIP animation technique--derived from First, Last, Invert, Play. This describes how the directive works. It measures the styling of the animate element before a layout change (first) and after a layout change (last). Then it inverts the last layout such that it matches the first layout. Finally it plays an animation which removes the inverted layout such that the element animates to the "last" layout. See the FLIP article by Paul Lewis for more information about the technique.

The directive uses a reactive controller to coordinate measuring the DOM of the animate element. The first layout is measured when the hosting element updates, and the last layout is measured when the hosting element renders and completes its update.

Usage

Here's an example:

import {animate} from '@lit-labs/motion';
// ...

class MyElement extends LitElement {
  static properties = {shifted: {}};
  static styles = css`
    .box {
      position: absolute;
      width: 100px;
      height: 100px;
      background: steelblue;
      top: 100px;
      border-radius: 50%;
    }

    .shifted {
      right: 0;
    }
  `;

  render() {
    return html`
      <button @click=${this._toggle}>Move</button>
      <div class="box ${this.shifted ? 'shifted' : ''}" ${animate()}></div>
    `;
  }

  _toggle() {
    this.shifted = !this.shifted;
  }
}

AnimateController

The animate controller allows you to coordinate and control animate directives within a given element.

The controller constructor takes an options object with the following properties:

Property	Usage
defaultOptions	default options for all element animate directives
startPaused	all element animations start paused
disabled	disables all element animations
onComplete	run when all element animations complete for a given update

The animate controller also provides API for controlling animate animations, including play(), pause(), cancel(), finish(), and togglePlay(). These methods affect all the animate animations for a given element. Finally, animate controller has properties which reflect the state of the animate animations in the host element: isPlaying returns true if any animate's are currently playing; isAnimating returns true if any animates currently have animations (which may be paused).

Contributing

Please see CONTRIBUTING.md.