Shifty is a tweening engine for JavaScript. It is a lightweight library meant to be encapsulated by higher level tools. At its core, Shifty provides:

• Interpolation of Numbers over time (tweening)
• Playback control of an individual tween
• Extensibility hooks for key points in the tweening process

This is useful because it is the least amount of functionality needed to build customizable animations. Shifty is optimized to run many times a second with minimal processing and memory overhead, which is necessary to achieve smooth animations.

npm install --save shifty

Shifty officially supports Evergreen browsers, Safari, and Node. If you encounter a browser-specific bug, please open an issue about it!

Shifty is compatible with IE11 (possibly older versions as well), but you will need to provide your own polyfills for it to work. If you are using https://polyfill.io/, you just need the es6 features enabled:

https://polyfill.io/v3/polyfill.min.js?features=es6

Here's a polyfilled demo of Shifty that works with IE11. Please see issue #113 for background on this.

First, install the dependencies via npm like so:

npm install

Once those are installed, you can generate dist/shifty.js with:

npm run build

To run the tests:

npm test

To generate the documentation (dist/doc):

npm run doc

To generate live documentation in your browser:

npm run doc:live

Shifty exposes a UMD module, so you can load it however you like:

// ES6
import { tween } from 'shifty';

Or:

// AMD
define(['shifty'], function(shifty) {
  shifty.tween({ from: { x: 0 }, to: { x: 10 } });
});

Or even:

// CommonJS
// Shifty is packaged for ES6 environments, so it exposes an object called
// `shifty`. To use it with CommonJS loaders (like Node's `require`), access
// the properties within that object.
const shifty = require('shifty').shifty;

shifty.tween({ from: { x: 0 }, to: { x: 10 } });

Please see the Getting Started guide and check out the API documentation.

Take a peek at the Network page to see all of the Shifty contributors.

Special thanks goes to Thomas Fuchs: Shifty's easing formulas and Bezier curve code was adapted from his awesome Scripty2 project.

Shifty is distributed under the MIT license. You are encouraged to use and modify the code to suit your needs, as well as redistribute it.