Rethink declarative animation

  1. Introduction
  2. Real World Declartive Animation
    1. Angular
    2. Anijs
    3. Vuejs
    4. React
    5. Summary
  3. An Even Better Solution for declarative animation!
    1. Question 1: When the animation start
      1. however, how to hook the enter and leave time on element?
      2. Is there any other trigger?
    2. Question 2: How to make the animation chainable?
    3. Question 3: How to animation two element step by step?
    4. Question 4: Is there any other buildin command?
    5. Question 5: How to extend Custom Command?
    6. Question 6: Need An compeletely Example?
  4. End
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Today, beacuse of new trends like material design and motion design, the animation is become more and more important in web-development.

On the other hand, thanks for the standardized web-component and frameworks like angularjs, knockoutjs, reactjs and vuejs etc. building the view of application in declartive way is coming into popular .

So, what about declarative animation?

This article serves to demonstrate an even better solution for declarative animation. before diving into detail, let’s first check ‘Real World Declartive Animation’ .

Real World Declartive Animation

This section will introduce the exsited approaches to implement declarative animation


angular is the most popular framework that have nearly 27000 stars on github now.

in angularjs, animation support is based on the module ngAnimate . The directives that support animation automatically are: ngRepeat, ngInclude, ngIf, ngSwitch, ngShow, ngHide, ngView and ngClass.

you need to define the appropriate CSS classes or to register a JavaScript animation via the module.animation() function.


<style type="text/css">, {
-webkit-transition:0.5s linear all;
transition:0.5s linear all;
} { } /* starting animations for enter */ { } /* terminal animations for enter */ { } /* starting animations for leave */ { } /* terminal animations for leave */
the animate service will automatically add .ng-enter and .ng-leave to the element
to trigger the CSS transition/animations
<div class="slide" ng-if="Expression"></div>

when the Expression is evaluated to true, the classng-enter is added first to prepares initial state, then ng-enter-active is added at nextReflow(similar with setTimeout(0)).


Anijs: Declarative handling library for CSS animations.

anijs’s main objective is to provide an eloquent, easy to translate, and quick to develop environment based on css animations.


<div id="main" data-anijs="if: DOMContentLoaded, on: document, do: swing animated, after: holdAnimClass"></div>

the exmpale above means:

when DOMContentLoaded triggered on document, addClass swing animated, then hold them after animationend(or transitionend).

It is dead simple and intuitive. the only requirement is to include a 8kb jsfile(minified, no gzip).


vuejs’s animation-support is very lightweight. just like angular, it hooks the element’s lifecycle at enter and leave (based on directive, e.g. v-if). you can use three directive to customize your animation

  1. v-animation animation based on class and animation
  2. v-transition: animation based on class and transition
  3. v-effect: custom animation extension.

use animation or transition

<p class="animated" v-if="show" v-animation>Look at me!</p>
<p class="msg" v-if="show" v-transition>Hello!</p>

use custom effect

<p v-effect="my-effect"></p>
Vue.effect('my-effect', {
enter: function (el, insert, timeout) {
// insert() will actually insert the element
leave: function (el, remove, timeout) {
// remove() will actually remove the element

To be honest, I don’t know why vuejs make distinguish between these three cases.


React’s animation support is based on the low-level API: ReactTransitionGroup. you can check the introduction of ReactCSSTransitionGroup(High-level API) on its animation page


/** @jsx React.DOM */
var ReactCSSTransitionGroup = React.addons.CSSTransitionGroup;
var TodoList = React.createClass({
// ignored some methods for short
render: function() {
var items =, i) {
return (
<div key={item} onClick={this.handleRemove.bind(this, i)}>
return (
<button onClick={this.handleAdd}>Add Item</button>
<ReactCSSTransitionGroup transitionName="example">

The element that wrapped by ReactCSSTransitionGroup can animate when it is injected to or leave from the component. it will get the example-enter CSS class and the example-enter-active CSS class added in the next tick (similar with angular). This is a convention based on the transitionName prop.


compare with the JavaScript-Based Animation(e.g. Velocity.js or jquery), the declarative animation that introduced above is obviously less flexible. for example:

  1. only works in given environment .(e.g. when element enter or leave)
  2. can not chainable
  3. can not combine with other elements’s animation
  4. developer know nothing about the phase of the animation. (image that you need do some work in javascript when the animation is done)

An Even Better Solution for declarative animation!

The solution introduced later that has been implemented in regularjs yet. and it can be full-supported by any framework that is data-driven(e.g. angularjs, vuejs, ractivejs..).

the solution is based on single directive: r-animation.


<div r-animation="Sequence"></div>
Command (";" Command)*
CommandName":" Param
CommandName: [-\w]+
Param: [^;]+

The following sections will raise several questions and solve them later by r-animation.

please be a patience man until compelete the rest of the page, you will find the power of r-animation !

the examples will depend on awesome animate.css for some css-related animation.

Question 1: When the animation start

There are two types of Command: 1. trigger 2. step.

trigger is used to trigger a animation sequence. and step is used to define a single animation.

Command on (trigger): when specified event is triggered , starting the animation.

<div r-animation="on: click; class: animated swing;"> </div>

this example means:

  1. when the element is clicked, trigged the animations.
  2. Command class will addclass animated swing(maybe trigger animation) to element, when the animationend(or transitionend) triggered, remove the class.
  3. animation done

however, how to hook the enter and leave time on element?

regularjs emit the mock enter and leave event for hooking the element’s lifycle, you can also use on to handle it;

<div class='box' r-hide= r-animation="
on: enter; class: animated bounceIn;
on: leave; class: animated bounceOut">
Box: enter

it is valid that defining multiply trigger on single r-animation. every trigger will create new animtion sequence.

Is there any other trigger?

now , we can take advantage of the data-driven framework to implement a more flexible command than on .

Command when (trigger): when the specifed Expression is evaluated to true, starting the animation.

<div class='box box-2' r-animation="when: test === true; class: animated swing">
Box2: triggered when test === true

when the test === true is computed to true, the animation will start.

Result on Codepen

Question 2: How to make the animation chainable?

r-animation is born to support chainable animation,you can simply sepecify multiply steps after one trigger.


<div class='box' r-animation=
class: animated swing;
class: animated shake;
class: animated bounceOut;
class: animated bounceIn;
click me

now, you will see the steps animate one by one.

Result on Codepen

Question 3: How to animation two element step by step?

Thanks for the data-driven system. you can use the call command for evaluating a Expression. after evaluating, the digest phase(regularjs is also based on dirty-check) will be automately triggered, it can trigger other animation (work with when).

Command call: evaluted a Expression, then enter the component’s digest phase. finaly step to next animation.


<div class='box animated' r-animation=
class: swing ;
call: otherSwing=true ;
class: shake">
box1: trigger by checkbox
<div class='box animated' r-animation=
"when: otherSwing;
class: swing;
">box2: after box1 swing</div>

steps as follow:

  1. when test is computed to true, start box1’s animation
  2. swing then call otherSwing = true;
  3. box2’s otherSwing is evaluted to true.
  4. box2 shakes, meanwhile box1 shakes;
  5. done.

Result on Codepen

thanks for call and data-driven system, we can staying competitive with javascript based animation on control.

Question 4: Is there any other buildin command?

  • wait: delay for next animation


<div class='box animated' r-animation=
class: swing ;
wait: 2000 ;
class: shake">
wait: click me

the example means: after clicking, swing then waiting 2000ms, finally shake.

  • style: set style and waiting the transitionend (if the style trigger the transition)


<div class='box animated' r-animation=
"on: click;
class: swing;
style: color #333;
class: bounceOut;
style: display none;
">style: click me </div>

add transition to make color fading effect work.

transition: color 1s linear;

example means: after clicking, swing then set style.color=#333(trigger transition)…

Result on Codepen

you can also extend custom command by your self.

Question 5: How to extend Custom Command?

you can extend javascript-based Animation via Component.animation(name, handle).

for example, we need fading animation.

Regular.animation("fade", function(step){
var param = step.param,
element = step.element,
fadein = param === "in",
step = fadein? 1.05: 0.9;
return function(done){
var start = fadein? 0.01: 1;
var tid = setInterval(function(){
start *= step
if(fadein && 1- start < 1e-3){
start = 1;
}else if(!fadein && start < 1e-3){
start = 0;
} = start;
}, 1000 / 60)

describe in template

<div class='box animated' r-animation=
class: swing ;
fade: out ;
fade: in;
fade: click me

the only thing you need to do is that: when your animation is compelete, call the function done.

Result on Codepen

you can also check the builtin’s sourcecode on github. it is realy dead simple!

Question 6: Need An compeletely Example?

let’s create a infinite animation for joke.

<div class='box animated' r-animation=
class: shake;
call: test=2 ;"
<div class='box animated' r-animation=
"when: test==2;
class: bounce;
call: test=3;
">box2: bounce</div>
<div class='box animated' r-animation=
"when: test==3;
class: swing;
call: test=1;
">box2: swing</div>

just as the logic described by the template. the sequence will never stopped.

Result on Codepen


if the post is helpful to you, gives regularjs a star