A keyframe animation library for JavaScript.
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Rekapi - Keyframes for JavaScript

Rekapi is a keyframe animation library for JavaScript. It gives you:

  • A keyframe-based Model by which to structure an animation
  • Controller APIs to control the playback of an animation

Rekapi does not define drawing methods. That part is completely generic, and the library exposes a common interface for defining Views.

Rekapi has two dependencies: Underscore and Shifty.

Rekapi has been tested in and supports:

  • Modern HTML5 browsers
  • IE 7/8 (9 probably works; has not been tested)
  • Node.js

Please note: Rekapi is a rewrite of Kapi. Rekapi is very similar to Kapi, but they are not identical. Rekapi is not a drop-in replacement for Kapi. Rekapi is way awesomer, so you should use it instead.

The API may change somewhat before reaching 1.0. See how to upgrade from older versions. .

Please see the getting started guide .

What is keyframing?

Keyframing is an animation technique for defining states at specific points in time. Animations are always rendered as frames to the screen, and keyframing allows you to define the key points at which the motion in the animation changes - all of the frames that exist between those points are interpolated for you. It is a powerful way to construct a complex animation.

How do I use Rekapi?

A Rekapi animation is structured into a Model and Views, with Controller methods to manage the playback. Its usage boils down to four steps:

  • Define some Kapi.Actor Views
  • Instantiate and add the Views to a Kapi Model instance
  • Define keyframes (states) for the View instances
  • Play the animation with the Controller methods

Model - Kapi

The Model maintains the state of an animation. Rekapi's Model is represented by the Kapi Object. The Model controls the state of the animation and renders the Views.

View - Kapi.Actor

The Actors are the individual components of an animation. If you want to move a circle from left to right in your animation, that circle is an Actor. If you want to add a square to your animation that moves up and down, that square is another, separate actor. Actors are represented by the Kapi.Actor Object and its subclasses.

Controller methods

There are numerous Controller-type methods attached to the Kapi Object. These methods include play(), pause() and stop().


Rekapi works by passing data from a Model to a View. The View then renders the data based on a context. Rekapi treats contexts generically, and you can add more as you need them. Currently, the standard Rekapi build includes rendering contexts for the DOM and <canvas>.

A Rekapi context does two things: It extends the prototype of the standard Rekapi Objects (Kapi, Kapi.Actor), and it subclasses Kapi.Actor. This is how Rekapi renders to the <canvas> and DOM: The Canvas and DOM renderers create Kapi.CanvasActor and Kapi.DOMActor, respectively.

The Kapi.Actor base class only renders raw data, it doesn't represent data visually because it doesn't have a context. Use Kapi.DOMActor and Kapi.CanvasActor to render to the screen.


Alternatively, you can load Rekapi as an AMD module by using a loader such as RequireJS. This has the added benefit of not creating any Kapi, Tweenable (from Shifty) or _ global variables, unlike in the previous code samples.

Caution: You can only require rekapi.js or rekapi.min.js as AMD modules. It will not work with rekapi.bundle.min.js.

Here is an example of how you can use it with RequireJS:

// This example assumes that there is a `lib` directory in your project
  paths: {
    shifty: "lib/shifty",
    underscore: "lib/underscore.min",
    rekapi: "lib/rekapi"

// Dependencies (Underscore and Shifty) are automatically loaded.
require(['rekapi'], function(Kapi) {
  var kapi = new Kapi();


Rekapi can be used in Node.js. This can be useful for generating keyframe data. Usage is the same as in the browser. Loading the code requires the r.js script and looks a lot ike the AMD approach above:

var r = require('lib/r.js');
  paths: {
    shifty: "dist/shifty",
    underscore: "dist/underscore",
    rekapi: "dist/rekapi"

r(['rekapi'], function(Kapi) {
  var kapi = new Kapi();



If you find any bugs, have suggestions or questions, please post them them to the Rekapi Github issue tracker.

Building and contributing

If you'd like to download entirety of this repo, please note that it uses Git submodules. You will need to clone it like so:

$: git clone --recursive git@github.com:jeremyckahn/rekapi.git

The --recursive flag tells Git to download the submodules in addition to the Rekapi files. You will need these submodules in order to build Rekapi or run the tests.

If you make a change to the Rekapi source and would like to build the project, just run this from the Rekapi root directory on the command line:

sh build.sh <version> [<local_compiler_path>]

version is whatever version you want to call the build. Rekapi uses the SemVer versioning scheme. This will generate any files you need and place them into the dist/ directory. You can specify a local copy of the Google Closure compiler with local_compiler_path, if you have it. If you omit the local_compiler_path variable, then the script will curl out to the Closure compiler on the web. This will just work if you are on a Mac. On Linux, you may need run sudo apt-get install curl.

It's also important to make sure you didn't break any tests in tests/. You can take a quick look by opening tests/test.all_unit_tests.html in your browser.

Please make sure to follow the [style guide] (https://github.com/jeremyckahn/rekapi/blob/master/docs/styleguide.md).