A teeny tiny tweening engine in JavaScript.


Shifty - A teeny tiny tweening engine in JavaScript

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.

Browser compatibility

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


npm install --save shifty

Developing Shifty

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 in CLI:

npm test

To generate the documentation (dist/doc):

npm run doc

To generate, live-update, and view the documentation in your browser:

npm run doc:live

To start a development server:

npm start

Once that's running, you can run the tests at http://localhost:9009/test/.

Loading Shifty

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

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


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

Or even:

// CommonJS
const shifty = require('shifty');

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

Using Shifty

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.